From 637ca27332ea6e91456d2d8438a7ce641fb56f08 Mon Sep 17 00:00:00 2001
From: CB <8658089-monospace-dev@users.noreply.gitlab.com>
Date: Wed, 8 Apr 2026 12:26:41 +0200
Subject: [PATCH] Fix i18n locale loading for regional codes (de-DE, en-US,
 etc.)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

- fixes issue #6257
- Switch load strategy from 'currentOnly' to 'languageOnly' to normalize
  regional locale codes (de-DE → de) matching available backend files
- Simplify fallbackLng to static array since normalization is automatic
- Add error handling to i18n.changeLanguage() to prevent crashes on
  locale load failures
---
 app/javascript/App.jsx  |  9 +++++++--
 app/javascript/i18n.jsx | 11 ++---------
 2 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/app/javascript/App.jsx b/app/javascript/App.jsx
index f8a33f3400..4ea9f49641 100644
--- a/app/javascript/App.jsx
+++ b/app/javascript/App.jsx
@@ -85,8 +85,13 @@ export default function App() {
   // i18n
   const { i18n } = useTranslation();
   useEffect(() => {
-    i18n.changeLanguage(currentUser?.language);
-  }, [currentUser?.language]);
+    if (currentUser?.language) {
+      i18n.changeLanguage(currentUser.language).catch(() => {
+        // Silently fall back to default language if change fails
+        console.warn(`Failed to load language: ${currentUser.language}`);
+      });
+    }
+  }, [currentUser?.language, i18n]);
 
   // Greenlight V3 brand-color theming
   const { isLoading, data: brandColors } = useSiteSetting(['PrimaryColor', 'PrimaryColorLight']);
diff --git a/app/javascript/i18n.jsx b/app/javascript/i18n.jsx
index 9856fc8b36..a1497de922 100644
--- a/app/javascript/i18n.jsx
+++ b/app/javascript/i18n.jsx
@@ -25,14 +25,7 @@ i18next
     backend: {
       loadPath: `${process.env.RELATIVE_URL_ROOT}/api/v1/locales/{{lng}}.json`,
     },
-    load: 'currentOnly',
-    fallbackLng: (locale) => {
-      const fallbacks = [];
-      if (locale?.indexOf('-') > -1) {
-        fallbacks.push(locale.split('-')[0]);
-      }
-      fallbacks.push('en');
-      return fallbacks;
-    },
+    load: 'languageOnly',
+    fallbackLng: ['en'],
   });
 export default i18next;