diff --git a/packages/app/supported-languages/package.json b/packages/app/supported-languages/package.json
index 6d2be3feb..b5504ee60 100644
--- a/packages/app/supported-languages/package.json
+++ b/packages/app/supported-languages/package.json
@@ -23,8 +23,6 @@
     },
     "scripts": {
         "build": "rimraf dist && tsc --project tsconfig.build.json",
-        "dev": "tsc --watch",
-        "clean": "rimraf dist .eslintcache",
         "lint": "biome check . && tsc",
         "lint:fix": "biome check --write",
         "test": "vitest run",
@@ -36,9 +34,7 @@
     "devDependencies": {
         "@biomejs/biome": "^2.3.7",
         "@lokalise/biome-config": "^3.1.0",
-        "@lokalise/node-core": "^14.0.0",
         "@lokalise/tsconfig": "^3.1.0",
-        "@rollup/plugin-typescript": "^12.1.0",
         "@vitest/coverage-v8": "^4.0.15",
         "rimraf": "^6.0.1",
         "typescript": "5.9.3",
diff --git a/packages/app/supported-languages/src/constants/index.spec.ts b/packages/app/supported-languages/src/constants/index.spec.ts
new file mode 100644
index 000000000..3bd0df988
--- /dev/null
+++ b/packages/app/supported-languages/src/constants/index.spec.ts
@@ -0,0 +1,38 @@
+import { describe, expect, it } from 'vitest'
+import {
+  getAllLanguages,
+  getAllRegions,
+  getAllScripts,
+  getLokaliseSupportedLanguagesAndLocales,
+  getStandardLocales,
+} from './index.ts'
+
+describe('getAllLanguages', () => {
+  it('returns a non-empty array', () => {
+    expect(getAllLanguages().length).toBeGreaterThan(0)
+  })
+})
+
+describe('getAllRegions', () => {
+  it('returns a non-empty array', () => {
+    expect(getAllRegions().length).toBeGreaterThan(0)
+  })
+})
+
+describe('getAllScripts', () => {
+  it('returns a non-empty array', () => {
+    expect(getAllScripts().length).toBeGreaterThan(0)
+  })
+})
+
+describe('getStandardLocales', () => {
+  it('returns a non-empty array', () => {
+    expect(getStandardLocales().length).toBeGreaterThan(0)
+  })
+})
+
+describe('getLokaliseSupportedLanguagesAndLocales', () => {
+  it('returns a non-empty array', () => {
+    expect(getLokaliseSupportedLanguagesAndLocales().length).toBeGreaterThan(0)
+  })
+})
diff --git a/packages/app/supported-languages/src/constants/index.ts b/packages/app/supported-languages/src/constants/index.ts
new file mode 100644
index 000000000..f38875629
--- /dev/null
+++ b/packages/app/supported-languages/src/constants/index.ts
@@ -0,0 +1,12 @@
+import { languages } from './languages.ts'
+import { lokaliseSupportedLanguagesAndLocales } from './lokalise-languages.ts'
+import { regions } from './regions.ts'
+import { scripts } from './scripts.ts'
+import { standardLocales } from './standard-locales.ts'
+
+export const getAllLanguages = () => Array.from(languages)
+export const getAllRegions = () => Array.from(regions)
+export const getAllScripts = () => Array.from(scripts)
+export const getStandardLocales = () => Array.from(standardLocales)
+export const getLokaliseSupportedLanguagesAndLocales = () =>
+  Array.from(lokaliseSupportedLanguagesAndLocales)
diff --git a/packages/app/supported-languages/src/languages.ts b/packages/app/supported-languages/src/constants/languages.ts
similarity index 98%
rename from packages/app/supported-languages/src/languages.ts
rename to packages/app/supported-languages/src/constants/languages.ts
index d30896d23..435f11d78 100644
--- a/packages/app/supported-languages/src/languages.ts
+++ b/packages/app/supported-languages/src/constants/languages.ts
@@ -12,7 +12,7 @@
  *
  * @link https://cldr.unicode.org/index
  */
-export const languages = [
+export const languages = new Set([
   'aa', // Afar
   'ab', // Abkhazian
   'ace', // Achinese
@@ -649,8 +649,4 @@ export const languages = [
   'zun', // Zuni
   'zxx', // No linguistic content
   'zza', // Zaza
-]
-
-export const languagesSet: ReadonlySet<string> = new Set(languages)
-
-export type Language = (typeof languages)[number]
+])
diff --git a/packages/app/supported-languages/src/constants/lokalise-languages.spec.ts b/packages/app/supported-languages/src/constants/lokalise-languages.spec.ts
new file mode 100644
index 000000000..a4c1dd020
--- /dev/null
+++ b/packages/app/supported-languages/src/constants/lokalise-languages.spec.ts
@@ -0,0 +1,14 @@
+import { describe, expect, it } from 'vitest'
+import { languages } from './languages.ts'
+import { lokaliseSupportedLanguagesAndLocales } from './lokalise-languages.ts'
+import { standardLocales } from './standard-locales.ts'
+
+describe('lokaliseSupportedLanguagesAndLocales', () => {
+  it('is a subset of all languages and standard locales', () => {
+    for (const entry of lokaliseSupportedLanguagesAndLocales) {
+      const isLanguage = languages.has(entry)
+      const isLocale = standardLocales.has(entry)
+      expect(isLanguage || isLocale).toBe(true)
+    }
+  })
+})
diff --git a/packages/app/supported-languages/src/lokaliseLanguages.ts b/packages/app/supported-languages/src/constants/lokalise-languages.ts
similarity index 98%
rename from packages/app/supported-languages/src/lokaliseLanguages.ts
rename to packages/app/supported-languages/src/constants/lokalise-languages.ts
index c6db0056b..00cf93866 100644
--- a/packages/app/supported-languages/src/lokaliseLanguages.ts
+++ b/packages/app/supported-languages/src/constants/lokalise-languages.ts
@@ -1,5 +1,5 @@
 // Subset of CLDR43 languages and standard locales that are supported by Lokalise
-export const lokaliseSupportedLanguagesAndLocales = [
+export const lokaliseSupportedLanguagesAndLocales = new Set([
   // Subset of CLDR43 languages that are supported by Lokalise
   'ru',
   'en',
@@ -382,4 +382,4 @@ export const lokaliseSupportedLanguagesAndLocales = [
   'fil-PH',
   'bs-Latn-BA',
   'ca-ES',
-]
+])
diff --git a/packages/app/supported-languages/src/regions.ts b/packages/app/supported-languages/src/constants/regions.ts
similarity index 98%
rename from packages/app/supported-languages/src/regions.ts
rename to packages/app/supported-languages/src/constants/regions.ts
index a26587f73..f8fde29c7 100644
--- a/packages/app/supported-languages/src/regions.ts
+++ b/packages/app/supported-languages/src/constants/regions.ts
@@ -8,7 +8,7 @@
  *
  * @link https://cldr.unicode.org/index
  */
-export const regions = [
+export const regions = new Set([
   '001', // World
   '002', // Africa
   '003', // North America
@@ -304,8 +304,4 @@ export const regions = [
   'ZM', // Zambia
   'ZW', // Zimbabwe
   'ZZ', // Unknown Region
-]
-
-export const regionsSet: ReadonlySet<string> = new Set(regions)
-
-export type Region = (typeof regions)[number]
+])
diff --git a/packages/app/supported-languages/src/constants/rtl-languages.spec.ts b/packages/app/supported-languages/src/constants/rtl-languages.spec.ts
new file mode 100644
index 000000000..7c19f910b
--- /dev/null
+++ b/packages/app/supported-languages/src/constants/rtl-languages.spec.ts
@@ -0,0 +1,11 @@
+import { describe, expect, it } from 'vitest'
+import { languages } from './languages.ts'
+import { rtlLanguages } from './rtl-languages.ts'
+
+describe('rtlLanguages', () => {
+  it('is a subset of all languages', () => {
+    for (const entry of rtlLanguages) {
+      expect(languages.has(entry)).toBe(true)
+    }
+  })
+})
diff --git a/packages/app/supported-languages/src/constants/rtl-languages.ts b/packages/app/supported-languages/src/constants/rtl-languages.ts
new file mode 100644
index 000000000..671412b56
--- /dev/null
+++ b/packages/app/supported-languages/src/constants/rtl-languages.ts
@@ -0,0 +1,26 @@
+/**
+ * Set of language subtags that use right-to-left script by default.
+ * Used to determine text direction without relying on Intl.Locale.getTextInfo(),
+ * which is not supported in Firefox.
+ *
+ * @link https://www.w3.org/International/questions/qa-scripts
+ */
+export const rtlLanguages = new Set([
+  'ar', // Arabic
+  'arc', // Aramaic
+  'ckb', // Central Kurdish (Sorani)
+  'dv', // Dhivehi
+  'fa', // Persian (Farsi)
+  'ha', // Hausa (Ajami)
+  'he', // Hebrew
+  'khw', // Khowar
+  'ks', // Kashmiri
+  'ku', // Kurdish (Arabic script)
+  'nqo', // N'Ko
+  'ps', // Pashto
+  'sd', // Sindhi
+  'syr', // Syriac
+  'ug', // Uyghur
+  'ur', // Urdu
+  'yi', // Yiddish
+])
diff --git a/packages/app/supported-languages/src/scripts.ts b/packages/app/supported-languages/src/constants/scripts.ts
similarity index 97%
rename from packages/app/supported-languages/src/scripts.ts
rename to packages/app/supported-languages/src/constants/scripts.ts
index c29d4c253..c45f67123 100644
--- a/packages/app/supported-languages/src/scripts.ts
+++ b/packages/app/supported-languages/src/constants/scripts.ts
@@ -8,7 +8,7 @@
  *
  * @link https://cldr.unicode.org/index
  */
-export const scripts = [
+export const scripts = new Set([
   'Adlm', // Adlam
   'Afak', // Afaka
   'Aghb', // Caucasian Albanian
@@ -211,8 +211,4 @@ export const scripts = [
   'Zxxx', // Unwritten
   'Zyyy', // Common
   'Zzzz', // Unknown Script
-]
-
-export const scriptsSet: ReadonlySet<string> = new Set(scripts)
-
-export type Script = (typeof scripts)[number]
+])
diff --git a/packages/app/supported-languages/src/standard-locales.test.ts b/packages/app/supported-languages/src/constants/standard-locales.spec.ts
similarity index 100%
rename from packages/app/supported-languages/src/standard-locales.test.ts
rename to packages/app/supported-languages/src/constants/standard-locales.spec.ts
diff --git a/packages/app/supported-languages/src/standard-locales.ts b/packages/app/supported-languages/src/constants/standard-locales.ts
similarity index 97%
rename from packages/app/supported-languages/src/standard-locales.ts
rename to packages/app/supported-languages/src/constants/standard-locales.ts
index 2b3686e0c..7dfec811b 100644
--- a/packages/app/supported-languages/src/standard-locales.ts
+++ b/packages/app/supported-languages/src/constants/standard-locales.ts
@@ -1,5 +1,5 @@
 // Locales supported as default
-export const standardLocales = [
+export const standardLocales = new Set([
   'af-ZA', // Afrikaans - South Africa
   'am-ET', // Amharic - Ethiopia
   'ar-AE', // Arabic - U.A.E.
@@ -219,8 +219,4 @@ export const standardLocales = [
   'zh-SG', // Chinese - Singapore
   'zh-TW', // Chinese - Taiwan
   'zu-ZA', // Zulu
-] as const
-
-export type StandardLocale = (typeof standardLocales)[number]
-
-export const standardLocalesSet: ReadonlySet<string> = new Set(standardLocales)
+])
diff --git a/packages/app/supported-languages/src/display-names.spec.ts b/packages/app/supported-languages/src/display-names.spec.ts
new file mode 100644
index 000000000..517a58e7c
--- /dev/null
+++ b/packages/app/supported-languages/src/display-names.spec.ts
@@ -0,0 +1,63 @@
+import { describe, expect, it } from 'vitest'
+import { getLanguageNameInEnglish, getLocalisedLanguageName } from './display-names.ts'
+
+describe('getLanguageNameInEnglish', () => {
+  it('returns name for a language code', () => {
+    expect(getLanguageNameInEnglish('es')).toBe('Spanish')
+    expect(getLanguageNameInEnglish('en')).toBe('English')
+    expect(getLanguageNameInEnglish('fr')).toBe('French')
+  })
+
+  it('returns name for a language-region locale', () => {
+    expect(getLanguageNameInEnglish('en-US')).toBe('English (United States)')
+    expect(getLanguageNameInEnglish('pt-BR')).toBe('Portuguese (Brazil)')
+  })
+
+  it('returns name for a language-script-region locale', () => {
+    expect(getLanguageNameInEnglish('bs-Latn-BA')).toBe('Bosnian (Latin, Bosnia & Herzegovina)')
+    expect(getLanguageNameInEnglish('zh-Hans-CN')).toBe('Chinese (Simplified, China)')
+  })
+
+  it('returns null for an empty string', () => {
+    expect(getLanguageNameInEnglish('')).toBeNull()
+  })
+
+  it('returns null for an unsupported tag', () => {
+    expect(getLanguageNameInEnglish('3141516')).toBeNull()
+  })
+})
+
+describe('getLocalisedLanguageName', () => {
+  it('returns name in the destination language', () => {
+    expect(getLocalisedLanguageName('es', 'fr')).toBe('espagnol')
+    expect(getLocalisedLanguageName('en', 'de')).toBe('Englisch')
+    expect(getLocalisedLanguageName('fr', 'es')).toBe('francés')
+  })
+
+  it('returns name for a language-region locale', () => {
+    expect(getLocalisedLanguageName('en-US', 'fr')).toBe('anglais (États-Unis)')
+    expect(getLocalisedLanguageName('pt-BR', 'es')).toBe('portugués (Brasil)')
+  })
+
+  it('returns name for a language-script-region locale', () => {
+    expect(getLocalisedLanguageName('bs-Latn-BA', 'fr')).toBe(
+      'bosniaque (latin, Bosnie-Herzégovine)',
+    )
+  })
+
+  it('respects the languageDisplay option', () => {
+    expect(getLocalisedLanguageName('en-US', 'fr', { languageDisplay: 'dialect' })).toBe(
+      'anglais américain',
+    )
+  })
+
+  it('returns null for an invalid source tag', () => {
+    expect(getLocalisedLanguageName('', 'en')).toBeNull()
+    expect(getLocalisedLanguageName('3141516', 'en')).toBeNull()
+  })
+
+  it('returns null for an invalid destination tag', () => {
+    expect(getLocalisedLanguageName('fr', 'wow')).toBeNull()
+    expect(getLocalisedLanguageName('fr', '')).toBeNull()
+  })
+})
diff --git a/packages/app/supported-languages/src/display-names.ts b/packages/app/supported-languages/src/display-names.ts
new file mode 100644
index 000000000..773175ba8
--- /dev/null
+++ b/packages/app/supported-languages/src/display-names.ts
@@ -0,0 +1,35 @@
+import type { Locale } from './locale.ts'
+import { isSupportedLocale } from './locale.ts'
+
+export const getLocalisedLanguageName = (
+  tag: Locale,
+  destinationTag: Locale,
+  options?: Omit<Partial<Intl.DisplayNamesOptions>, 'type'>,
+): string | null => {
+  if (!isSupportedLocale(tag) || !isSupportedLocale(destinationTag)) {
+    return null
+  }
+
+  const displayNames = new Intl.DisplayNames([destinationTag], {
+    type: 'language',
+    languageDisplay: 'standard',
+    ...options,
+  })
+
+  try {
+    const displayName = displayNames.of(tag)
+
+    /* v8 ignore start */
+    if (!displayName || displayName === 'root') return null
+    /* v8 ignore stop */
+
+    return displayName
+  } catch {
+    /* v8 ignore start */
+    return null
+    /* v8 ignore stop */
+  }
+}
+
+export const getLanguageNameInEnglish = (tag: Locale): string | null =>
+  getLocalisedLanguageName(tag, 'en')
diff --git a/packages/app/supported-languages/src/either.ts b/packages/app/supported-languages/src/either.ts
index a98951700..e5c374ec1 100644
--- a/packages/app/supported-languages/src/either.ts
+++ b/packages/app/supported-languages/src/either.ts
@@ -16,11 +16,3 @@ type Right<U> = {
  * @see {@link https://antman-does-software.com/stop-catching-errors-in-typescript-use-the-either-type-to-make-your-code-predictable Further reading on motivation for Either type}
  */
 export type Either<T, U> = NonNullable<Left<T> | Right<U>>
-
-/***
- * Variation of Either, which may or may not have Error set, but always has Result
- */
-export type DefiniteEither<T, U> = {
-  error?: T
-  result: U
-}
diff --git a/packages/app/supported-languages/src/index.test.ts b/packages/app/supported-languages/src/index.test.ts
deleted file mode 100644
index 3c8129393..000000000
--- a/packages/app/supported-languages/src/index.test.ts
+++ /dev/null
@@ -1,235 +0,0 @@
-import { describe, expect, it } from 'vitest'
-import {
-  getCommonLanguagesForRegion,
-  getCommonRegionsForLanguage,
-  getLanguageNameInEnglish,
-  getLocalisedLanguageName,
-  getStandardLocales,
-  isStandardLocale,
-  isSupportedLocale,
-  normalizeLocale,
-  parseLocale,
-  stringifyLocale,
-} from './index.ts'
-
-describe('supported-languages package', () => {
-  describe('getStandardLocales', () => {
-    it('returns a list of languages', () => {
-      const languages = getStandardLocales()
-      expect(languages).toHaveLength(219)
-
-      expect(languages).toContain('da-DK')
-      expect(languages).toContain('en-US')
-      expect(languages).toContain('bs-Latn-BA')
-    })
-  })
-
-  describe('isStandardLocale', () => {
-    it('returns true for matching locales', () => {
-      expect(isStandardLocale('en-US')).toBe(true)
-      expect(isStandardLocale('fr-CA')).toBe(true)
-      expect(isStandardLocale('bs-Latn-BA')).toBe(true)
-    })
-
-    it('returns false for non-matching locales', () => {
-      expect(isStandardLocale('en')).toBe(false)
-      expect(isStandardLocale('en-DA')).toBe(false)
-      expect(isStandardLocale('foo')).toBe(false)
-    })
-  })
-
-  describe('isSupportedLocale', () => {
-    it('returns true for valid values', () => {
-      expect(isSupportedLocale('en')).toBe(true)
-      expect(isSupportedLocale('en-US')).toBe(true)
-      expect(isSupportedLocale('en-Latn-US')).toBe(true)
-      expect(isSupportedLocale('sr-Cyrl-CS')).toBe(true)
-
-      expect(isSupportedLocale('en-us')).toBe(true)
-      expect(isSupportedLocale('my')).toBe(true) // Burmese
-
-      expect(isSupportedLocale('en-RU')).toBe(true) // Valid Language and Region
-      expect(isSupportedLocale('en-001')).toBe(true) // 001 is a valid Region
-
-      expect(isSupportedLocale('en-1234')).toBe(true)
-      expect(isSupportedLocale('en-9999')).toBe(true)
-      expect(isSupportedLocale('en-00001')).toBe(true)
-
-      expect(isSupportedLocale('zh-CN-script')).toBe(true)
-      expect(isSupportedLocale('in-FRENCH')).toBe(true) // 'in' is identified as 'id' which is Indonesian
-      expect(isSupportedLocale('in-FILES')).toBe(true)
-      expect(isSupportedLocale('in-FILES-lalaland')).toBe(true)
-    })
-
-    it('returns false for invalid values', () => {
-      expect(isSupportedLocale('abc')).toBe(false) // invalid language
-      expect(isSupportedLocale('abc-US')).toBe(false) // invalid language
-      expect(isSupportedLocale('en-AB')).toBe(false) // invalid region
-      expect(isSupportedLocale('en-Abcd-US')).toBe(false) // invalid script
-    })
-  })
-
-  describe('getCommonRegionsForLanguage', () => {
-    it('returns list of regions for known languages', () => {
-      expect(getCommonRegionsForLanguage('zh')).toMatchObject(['CN', 'HK', 'MO', 'SG', 'TW'])
-    })
-
-    it('returns empty list for languages not in standard locales', () => {
-      expect(getCommonRegionsForLanguage('ace')).toMatchObject([])
-    })
-
-    it('returns empty list for unknown languages', () => {
-      expect(getCommonRegionsForLanguage('abc')).toMatchObject([])
-    })
-  })
-
-  describe('getCommonLanguagesForRegion', () => {
-    it('returns list of languages for known regions', () => {
-      expect(getCommonLanguagesForRegion('CA')).toMatchObject(['en', 'fr', 'iu'])
-    })
-
-    it('returns empty list for regions not in standard locales', () => {
-      expect(getCommonLanguagesForRegion('AC')).toMatchObject([])
-    })
-
-    it('returns empty list for unknown regions', () => {
-      expect(getCommonLanguagesForRegion('AB')).toMatchObject([])
-    })
-  })
-
-  describe('parseLocale', () => {
-    describe('with valid locale tags', () => {
-      it('parses language only', () => {
-        const { language, script, region } = parseLocale('en').result!
-        expect(language).toBe('en')
-        expect(script).toBeUndefined()
-        expect(region).toBeUndefined()
-      })
-
-      it('parses language and script', () => {
-        const { language, script, region } = parseLocale('en-Latn').result!
-        expect(language).toBe('en')
-        expect(script).toBe('Latn')
-        expect(region).toBeUndefined()
-      })
-
-      it('parses language and region', () => {
-        const { language, script, region } = parseLocale('en-US').result!
-        expect(language).toBe('en')
-        expect(script).toBeUndefined()
-        expect(region).toBe('US')
-      })
-
-      it('parses language, script and region', () => {
-        const { language, script, region } = parseLocale('en-Latn-US').result!
-        expect(language).toBe('en')
-        expect(script).toBe('Latn')
-        expect(region).toBe('US')
-      })
-
-      it('ignores additional subtags', () => {
-        const { language, script, region } = parseLocale('en-US-u-ca-gregory').result!
-        expect(language).toBe('en')
-        expect(script).toBeUndefined()
-        expect(region).toBe('US')
-      })
-    })
-
-    it('throws on unsupported value', () => {
-      expect(parseLocale('abc-AB').error).toBe('Locale tag abc-AB is not supported')
-    })
-  })
-
-  describe('stringifyLocale', () => {
-    it('stringifies language only', () => {
-      expect(stringifyLocale({ language: 'en' })).toBe('en')
-    })
-
-    it('stringifies language and script', () => {
-      expect(stringifyLocale({ language: 'en', script: 'Latn' })).toBe('en-Latn')
-    })
-
-    it('stringifies language and region', () => {
-      expect(stringifyLocale({ language: 'en', region: 'US' })).toBe('en-US')
-    })
-
-    it('stringifies language, script and region', () => {
-      expect(stringifyLocale({ language: 'en', script: 'Latn', region: 'US' })).toBe('en-Latn-US')
-    })
-  })
-
-  describe('normalizeLocale', () => {
-    it('normalizeLocale language', () => {
-      expect(normalizeLocale('en')).toBe('en')
-      expect(normalizeLocale('hello')).toBe('hello')
-    })
-
-    it('normalizeLocale language and script', () => {
-      expect(normalizeLocale('en-Latn')).toBe('en-Latn')
-    })
-
-    it('normalizeLocale language and region', () => {
-      expect(normalizeLocale('en-US')).toBe('en-US')
-      expect(normalizeLocale('en-RU')).toBe('en-RU')
-
-      expect(normalizeLocale('en-001')).toBe('en-001') // 001 is a valid Region
-
-      expect(normalizeLocale('en-1234')).toBe('en')
-      expect(normalizeLocale('en-9999')).toBe('en')
-      expect(normalizeLocale('en-00001')).toBe('en')
-      expect(normalizeLocale('en-hello')).toBe('en')
-
-      expect(normalizeLocale('in-FRENCH')).toBe('id') // 'in' is identified as 'id' which is Indonesian
-      expect(normalizeLocale('in-FILES')).toBe('id')
-    })
-
-    it('normalizeLocale language, script and region', () => {
-      expect(normalizeLocale('en-Latn-US')).toBe('en-Latn-US')
-      expect(normalizeLocale('zh-CN-script')).toBe('zh-CN') // script is ignored by Intl.Locale
-      expect(normalizeLocale('sr-Cyrl-CS')).toBe('sr-Cyrl-RS') // CS is converted to RS by Intl.Locale
-      expect(normalizeLocale('sr-Cyrl-RS')).toBe('sr-Cyrl-RS')
-      expect(normalizeLocale('in-FILES-lalaland')).toBe('id') // FILES and lalaland are ignored
-    })
-
-    it('normalizeLocale language is und', () => {
-      expect(normalizeLocale('und')).toBeNull()
-    })
-  })
-
-  describe('getLanguageNameInEnglish', () => {
-    it('get language name in English', () => {
-      expect(getLanguageNameInEnglish('es')).toBe('Spanish')
-      expect(getLanguageNameInEnglish('en')).toBe('English')
-      expect(getLanguageNameInEnglish('en-US')).toBe('English (United States)')
-      expect(getLanguageNameInEnglish('bs-Latn-BA')).toBe('Bosnian (Latin, Bosnia & Herzegovina)')
-    })
-
-    it('wrong tag', () => {
-      expect(getLanguageNameInEnglish('')).toBeNull()
-      expect(getLanguageNameInEnglish('3141516')).toBeNull()
-    })
-  })
-
-  describe('getLocalisedLanguageName', () => {
-    it('get language name in French', () => {
-      expect(getLocalisedLanguageName('es', 'fr')).toBe('espagnol')
-      expect(getLocalisedLanguageName('en-US', 'fr')).toBe('anglais (États-Unis)')
-      expect(getLocalisedLanguageName('en-US', 'fr', { languageDisplay: 'dialect' })).toBe(
-        'anglais américain',
-      )
-      expect(getLocalisedLanguageName('bs-Latn-BA', 'fr')).toBe(
-        'bosniaque (latin, Bosnie-Herzégovine)',
-      )
-    })
-
-    it('wrong tag', () => {
-      expect(getLocalisedLanguageName('', 'en')).toBeNull()
-      expect(getLocalisedLanguageName('3141516', 'en')).toBeNull()
-    })
-
-    it('wrong destination tag', () => {
-      expect(getLocalisedLanguageName('fr', 'wow')).toBeNull()
-      expect(getLocalisedLanguageName('fr', 'wow')).toBeNull()
-    })
-  })
-})
diff --git a/packages/app/supported-languages/src/index.ts b/packages/app/supported-languages/src/index.ts
index 0040cb400..464a77749 100644
--- a/packages/app/supported-languages/src/index.ts
+++ b/packages/app/supported-languages/src/index.ts
@@ -1,201 +1,4 @@
-import type { Either } from '@lokalise/node-core'
-import type { Language } from './languages.ts'
-import { languages, languagesSet } from './languages.ts'
-import { lokaliseSupportedLanguagesAndLocales } from './lokaliseLanguages.ts'
-import type { Region } from './regions.ts'
-import { regions, regionsSet } from './regions.ts'
-import type { Script } from './scripts.ts'
-import { scripts, scriptsSet } from './scripts.ts'
-import type { StandardLocale } from './standard-locales.ts'
-import { standardLocales, standardLocalesSet } from './standard-locales.ts'
-
-/**
- * String representation of a locale.
- */
-// eslint-disable-next-line @typescript-eslint/no-redundant-type-constituents
-export type LocaleString = Language | `${Language}-${Region}` | `${Language}-${Script}-${Region}`
-
-/**
- * Object representation of a locale.
- */
-export type LocaleObject = {
-  language: string
-  script?: string
-  region?: string
-}
-
-/**
- * Get list of all our standard locale codes.
- */
-export const getStandardLocales = () => {
-  return standardLocales
-}
-
-/**
- * Get list of all available languages we support.
- */
-export const getAllLanguages = () => {
-  return languages
-}
-
-/**
- * Get list of all available scripts we support.
- */
-export const getAllScripts = () => {
-  return scripts
-}
-
-/**
- * Get list of all available regions we support.
- */
-export const getAllRegions = () => {
-  return regions
-}
-
-export const getLokaliseSupportedLanguagesAndLocales = () => {
-  return lokaliseSupportedLanguagesAndLocales
-}
-
-/**
- * Determine if `tag` is part of our standard locales.
- */
-export const isStandardLocale = (tag: string): tag is StandardLocale => {
-  return standardLocalesSet.has(tag as StandardLocale)
-}
-
-/**
- * Parse locale string into object.
- *
- * @throws {RangeError} If locale is structurally invalid or values are not in our supported values
- */
-export const parseLocale = (tag: LocaleString): Either<string, LocaleObject> => {
-  if (!isSupportedLocale(tag)) {
-    return { error: `Locale tag ${tag} is not supported` }
-  }
-
-  const { language, script, region } = new Intl.Locale(tag)
-
-  return { result: { language, script, region } }
-}
-
-/**
- * Turn LocaleObject into LocaleString.
- */
-export const stringifyLocale = (obj: LocaleObject): LocaleString => {
-  return [obj.language, obj.script, obj.region].filter(Boolean).join('-')
-}
-
-/**
- * Verify that `tag` is a valid locale code and all parts of it is in our lists of supported values.
- */
-export const isSupportedLocale = (tag: string) => {
-  try {
-    const { language, script, region } = new Intl.Locale(tag)
-
-    if (region && !regionsSet.has(region)) {
-      return false
-    }
-
-    if (script && !scriptsSet.has(script)) {
-      return false
-    }
-
-    return languagesSet.has(language)
-  } catch (_) {
-    return false
-  }
-}
-
-/**
- * Get common regions for a language, based on our standard locales.
- */
-export const getCommonRegionsForLanguage = (() => {
-  const cache: Record<Language, Array<Region>> = {}
-
-  // Create a mapping of languages to common regions up front
-  for (const locale of standardLocales) {
-    const { language, region } = new Intl.Locale(locale)
-
-    if (!region) {
-      continue
-    }
-
-    const current = cache[language] ?? []
-    current.push(region)
-    cache[language] = current
-  }
-
-  return (language: string): Array<Region> => {
-    return cache[language] ?? []
-  }
-})()
-
-/**
- * Get common languages for a region, based on our standard locales.
- */
-export const getCommonLanguagesForRegion = (() => {
-  const cache: Record<Region, Array<Language>> = {}
-
-  // Create a mapping of languages to common regions up front
-  for (const locale of standardLocales) {
-    const { language, region } = new Intl.Locale(locale)
-
-    if (!region) {
-      continue
-    }
-
-    const current = cache[region] ?? []
-    current.push(language)
-    cache[region] = current
-  }
-
-  return (region: string): Array<Language> => {
-    return cache[region] ?? []
-  }
-})()
-
-export const normalizeLocale = (tag: string) => {
-  /**
-   * "und" is used in some systems to mean an "Unknown Language".
-   * Throughout our system however, we prefer to use "null" to mean unknown language.*
-   * */
-  if (tag === 'und') return null
-
-  try {
-    return stringifyLocale(new Intl.Locale(tag))
-  } catch (_) {
-    return null
-  }
-}
-
-export const getLanguageNameInEnglish = (tag: LocaleString): string | null => {
-  return getLocalisedLanguageName(tag, 'en')
-}
-
-export const getLocalisedLanguageName = (
-  tag: LocaleString,
-  destinationTag: LocaleString,
-  options?: Omit<Partial<Intl.DisplayNamesOptions>, 'type'>,
-): string | null => {
-  if (!isSupportedLocale(tag) || !isSupportedLocale(destinationTag)) {
-    return null
-  }
-
-  const displayNames = new Intl.DisplayNames([destinationTag], {
-    type: 'language',
-    languageDisplay: 'standard',
-    ...options,
-  })
-
-  try {
-    const displayName = displayNames.of(tag)
-
-    if (displayName === 'root') {
-      return null
-    }
-
-    return displayName ?? null
-  } catch (_) {
-    return null
-  }
-}
+export * from './constants/index.ts'
+export * from './display-names.ts'
+export * from './locale.ts'
+export * from './locale-lookup.ts'
diff --git a/packages/app/supported-languages/src/locale-lookup.spec.ts b/packages/app/supported-languages/src/locale-lookup.spec.ts
new file mode 100644
index 000000000..bf28b153a
--- /dev/null
+++ b/packages/app/supported-languages/src/locale-lookup.spec.ts
@@ -0,0 +1,34 @@
+import { describe, expect, it } from 'vitest'
+import { getCommonLanguagesForRegion, getCommonRegionsForLanguage } from './locale-lookup.ts'
+
+describe('getCommonRegionsForLanguage', () => {
+  it('returns regions for a language present in standard locales', () => {
+    expect(getCommonRegionsForLanguage('zh')).toMatchObject(['CN', 'HK', 'MO', 'SG', 'TW'])
+    expect(getCommonRegionsForLanguage('en')).toContain('US')
+    expect(getCommonRegionsForLanguage('en')).toContain('GB')
+  })
+
+  it('returns empty array for a language not present in standard locales', () => {
+    expect(getCommonRegionsForLanguage('ace')).toEqual([])
+  })
+
+  it('returns empty array for an unknown language', () => {
+    expect(getCommonRegionsForLanguage('abc')).toEqual([])
+  })
+})
+
+describe('getCommonLanguagesForRegion', () => {
+  it('returns languages for a region present in standard locales', () => {
+    expect(getCommonLanguagesForRegion('CA')).toMatchObject(['en', 'fr', 'iu'])
+    expect(getCommonLanguagesForRegion('CH')).toContain('de')
+    expect(getCommonLanguagesForRegion('CH')).toContain('fr')
+  })
+
+  it('returns empty array for a region not present in standard locales', () => {
+    expect(getCommonLanguagesForRegion('AC')).toEqual([])
+  })
+
+  it('returns empty array for an unknown region', () => {
+    expect(getCommonLanguagesForRegion('AB')).toEqual([])
+  })
+})
diff --git a/packages/app/supported-languages/src/locale-lookup.ts b/packages/app/supported-languages/src/locale-lookup.ts
new file mode 100644
index 000000000..8ac9c7c03
--- /dev/null
+++ b/packages/app/supported-languages/src/locale-lookup.ts
@@ -0,0 +1,49 @@
+import { standardLocales } from './constants/standard-locales.ts'
+
+/**
+ * Get common regions for a language, based on our standard locales.
+ */
+export const getCommonRegionsForLanguage = (() => {
+  const cache: Record<string, Array<string>> = {}
+
+  // Create a mapping of languages to common regions up front
+  for (const locale of standardLocales) {
+    const { language, region } = new Intl.Locale(locale)
+
+    if (!region) {
+      continue
+    }
+
+    const current = cache[language] ?? []
+    current.push(region)
+    cache[language] = current
+  }
+
+  return (language: string): Array<string> => {
+    return cache[language] ?? []
+  }
+})()
+
+/**
+ * Get common languages for a region, based on our standard locales.
+ */
+export const getCommonLanguagesForRegion = (() => {
+  const cache: Record<string, Array<string>> = {}
+
+  // Create a mapping of languages to common regions up front
+  for (const locale of standardLocales) {
+    const { language, region } = new Intl.Locale(locale)
+
+    if (!region) {
+      continue
+    }
+
+    const current = cache[region] ?? []
+    current.push(language)
+    cache[region] = current
+  }
+
+  return (region: string): Array<string> => {
+    return cache[region] ?? []
+  }
+})()
diff --git a/packages/app/supported-languages/src/locale.spec.ts b/packages/app/supported-languages/src/locale.spec.ts
new file mode 100644
index 000000000..7d81fdb54
--- /dev/null
+++ b/packages/app/supported-languages/src/locale.spec.ts
@@ -0,0 +1,175 @@
+import { describe, expect, it } from 'vitest'
+import { languages } from './constants/languages.ts'
+import { rtlLanguages } from './constants/rtl-languages.ts'
+import {
+  getLocaleDirection,
+  isStandardLocale,
+  isSupportedLocale,
+  normalizeLocale,
+  parseLocale,
+  stringifyLocale,
+} from './locale.ts'
+
+describe('isSupportedLocale', () => {
+  it('returns true for valid language codes', () => {
+    expect(isSupportedLocale('en')).toBe(true)
+    expect(isSupportedLocale('my')).toBe(true) // Burmese
+  })
+
+  it('returns true for valid language-region locales', () => {
+    expect(isSupportedLocale('en-US')).toBe(true)
+    expect(isSupportedLocale('en-RU')).toBe(true)
+    expect(isSupportedLocale('en-001')).toBe(true) // 001 is a valid region
+  })
+
+  it('returns true for valid language-script-region locales', () => {
+    expect(isSupportedLocale('en-Latn-US')).toBe(true)
+    expect(isSupportedLocale('sr-Cyrl-CS')).toBe(true)
+  })
+
+  it('is case-insensitive', () => {
+    expect(isSupportedLocale('en-us')).toBe(true)
+  })
+
+  it('returns false for an unknown language', () => {
+    expect(isSupportedLocale('abc')).toBe(false)
+    expect(isSupportedLocale('abc-US')).toBe(false)
+  })
+
+  it('returns false for an unknown region', () => {
+    expect(isSupportedLocale('en-AB')).toBe(false)
+  })
+
+  it('returns false for an unknown script', () => {
+    expect(isSupportedLocale('en-Abcd-US')).toBe(false)
+  })
+})
+
+describe('isStandardLocale', () => {
+  it('returns true for standard locales', () => {
+    expect(isStandardLocale('en-US')).toBe(true)
+    expect(isStandardLocale('fr-CA')).toBe(true)
+    expect(isStandardLocale('bs-Latn-BA')).toBe(true)
+  })
+
+  it('returns false for language-only codes', () => {
+    expect(isStandardLocale('en')).toBe(false)
+  })
+
+  it('returns false for non-standard locale combinations', () => {
+    expect(isStandardLocale('en-DA')).toBe(false)
+    expect(isStandardLocale('foo')).toBe(false)
+  })
+})
+
+describe('stringifyLocale', () => {
+  it('stringifies language only', () => {
+    expect(stringifyLocale({ language: 'en' })).toBe('en')
+  })
+
+  it('stringifies language and script', () => {
+    expect(stringifyLocale({ language: 'en', script: 'Latn' })).toBe('en-Latn')
+  })
+
+  it('stringifies language and region', () => {
+    expect(stringifyLocale({ language: 'en', region: 'US' })).toBe('en-US')
+  })
+
+  it('stringifies language, script and region', () => {
+    expect(stringifyLocale({ language: 'en', script: 'Latn', region: 'US' })).toBe('en-Latn-US')
+  })
+})
+
+describe('parseLocale', () => {
+  it('parses language only', () => {
+    const { language, script, region } = parseLocale('en').result!
+    expect(language).toBe('en')
+    expect(script).toBeUndefined()
+    expect(region).toBeUndefined()
+  })
+
+  it('parses language and script', () => {
+    const { language, script, region } = parseLocale('en-Latn').result!
+    expect(language).toBe('en')
+    expect(script).toBe('Latn')
+    expect(region).toBeUndefined()
+  })
+
+  it('parses language and region', () => {
+    const { language, script, region } = parseLocale('en-US').result!
+    expect(language).toBe('en')
+    expect(script).toBeUndefined()
+    expect(region).toBe('US')
+  })
+
+  it('parses language, script and region', () => {
+    const { language, script, region } = parseLocale('en-Latn-US').result!
+    expect(language).toBe('en')
+    expect(script).toBe('Latn')
+    expect(region).toBe('US')
+  })
+
+  it('ignores additional subtags', () => {
+    const { language, script, region } = parseLocale('en-US-u-ca-gregory').result!
+    expect(language).toBe('en')
+    expect(script).toBeUndefined()
+    expect(region).toBe('US')
+  })
+
+  it('returns error for an unsupported locale', () => {
+    expect(parseLocale('abc-AB').error).toBe('Locale tag abc-AB is not supported')
+  })
+})
+
+describe('getLocaleDirection', () => {
+  it.each([
+    ...Array.from(rtlLanguages).map((lang) => [lang, 'rtl'] as [string, 'rtl']),
+    ...Array.from(languages)
+      .filter((lang) => !rtlLanguages.has(lang))
+      .map((lang) => [lang, 'ltr'] as [string, 'ltr']),
+    ['ar-SA', 'rtl'],
+    ['en-US', 'ltr'],
+    ['not-a-valid-!!!-locale', null],
+    ['abc', null],
+  ])('getLocaleDirection(%s) → %s', (tag, expected) => {
+    expect(getLocaleDirection(tag)).toBe(expected)
+  })
+})
+
+describe('normalizeLocale', () => {
+  it('returns null for "und"', () => {
+    expect(normalizeLocale('und')).toBeNull()
+  })
+
+  it('returns null for invalid locale', () => {
+    expect(normalizeLocale('not a locale')).toBeNull()
+  })
+
+  it('normalizes language only', () => {
+    expect(normalizeLocale('en')).toBe('en')
+  })
+
+  it('normalizes language and script', () => {
+    expect(normalizeLocale('en-Latn')).toBe('en-Latn')
+  })
+
+  it('normalizes language and region', () => {
+    expect(normalizeLocale('en-US')).toBe('en-US')
+    expect(normalizeLocale('en-001')).toBe('en-001')
+  })
+
+  it('normalizes language, script and region', () => {
+    expect(normalizeLocale('en-Latn-US')).toBe('en-Latn-US')
+    expect(normalizeLocale('sr-Cyrl-CS')).toBe('sr-Cyrl-RS') // CS → RS via Intl.Locale
+  })
+
+  it('strips invalid subtags', () => {
+    expect(normalizeLocale('en-1234')).toBe('en')
+    expect(normalizeLocale('in-FRENCH')).toBe('id') // 'in' → 'id' (Indonesian)
+    expect(normalizeLocale('zh-CN-script')).toBe('zh-CN')
+  })
+
+  it('returns the tag as-is for structurally valid but unknown values', () => {
+    expect(normalizeLocale('hello')).toBe('hello')
+  })
+})
diff --git a/packages/app/supported-languages/src/locale.ts b/packages/app/supported-languages/src/locale.ts
new file mode 100644
index 000000000..e1ae0ff2b
--- /dev/null
+++ b/packages/app/supported-languages/src/locale.ts
@@ -0,0 +1,97 @@
+import { languages } from './constants/languages.ts'
+import { regions } from './constants/regions.ts'
+import { rtlLanguages } from './constants/rtl-languages.ts'
+import { scripts } from './constants/scripts.ts'
+import { standardLocales } from './constants/standard-locales.ts'
+import type { Either } from './either.ts'
+
+/**
+ * String representation of a locale.
+ */
+export type Locale = string | `${string}-${string}` | `${string}-${string}-${string}`
+/**
+ * @deprecated Use Locale instead
+ */
+export type LocaleString = Locale
+
+/**
+ * Object representation of a locale.
+ */
+export type LocaleObject = {
+  language: string
+  script?: string
+  region?: string
+}
+
+export type LanguageDirection = 'ltr' | 'rtl'
+
+/**
+ * Verify that `tag` is a valid locale code and all parts of it is in our lists of supported values.
+ */
+export const isSupportedLocale = (tag: Locale) => {
+  try {
+    const { language, script, region } = new Intl.Locale(tag)
+
+    if (region && !regions.has(region)) {
+      return false
+    }
+
+    if (script && !scripts.has(script)) {
+      return false
+    }
+
+    return languages.has(language)
+  } catch (_) {
+    return false
+  }
+}
+
+/**
+ * Determine if `tag` is part of our standard locales.
+ */
+export const isStandardLocale = (tag: Locale): boolean => standardLocales.has(tag)
+
+/**
+ * Turn LocaleObject into LocaleString.
+ */
+export const stringifyLocale = (obj: LocaleObject): Locale =>
+  [obj.language, obj.script, obj.region].filter(Boolean).join('-')
+
+/**
+ * Parse locale string into object.
+ *
+ * @throws {RangeError} If locale is structurally invalid or values are not in our supported values
+ */
+export const parseLocale = (tag: Locale): Either<string, LocaleObject> => {
+  if (!isSupportedLocale(tag)) {
+    return { error: `Locale tag ${tag} is not supported` }
+  }
+
+  const { language, script, region } = new Intl.Locale(tag)
+
+  return { result: { language, script, region } }
+}
+
+export const normalizeLocale = (tag: Locale) => {
+  /**
+   * "und" is used in some systems to mean an "Unknown Language".
+   * Throughout our system however, we prefer to use "null" to mean unknown language.*
+   * */
+  if (tag === 'und') return null
+
+  try {
+    return stringifyLocale(new Intl.Locale(tag))
+  } catch {
+    return null
+  }
+}
+
+export const getLocaleDirection = (tag: Locale): LanguageDirection | null => {
+  const parsedLocale = parseLocale(tag)
+
+  return parsedLocale.result
+    ? rtlLanguages.has(parsedLocale.result?.language)
+      ? 'rtl'
+      : 'ltr'
+    : null
+}
diff --git a/packages/app/supported-languages/vitest.config.ts b/packages/app/supported-languages/vitest.config.ts
index 1e482c119..596a828ba 100644
--- a/packages/app/supported-languages/vitest.config.ts
+++ b/packages/app/supported-languages/vitest.config.ts
@@ -10,7 +10,7 @@ export default defineConfig({
     coverage: {
       provider: 'v8',
       include: ['src/**/*.ts'],
-      exclude: ['src/index.ts'],
+      exclude: ['src/**/index.ts'],
       thresholds: {
         lines: 100,
         functions: 100,