diff --git a/frontend/package.json b/frontend/package.json
index 66cc8dbd..2b20a22e 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -16,9 +16,12 @@
     "@tanstack/react-virtual": "^3.13.23",
     "axios": "^1.7.2",
     "framer-motion": "^12.38.0",
+    "i18next": "^23.11.5",
+    "i18next-browser-languagedetector": "^8.0.0",
     "qrcode": "^1.5.4",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
+    "react-i18next": "^14.1.2",
     "recharts": "^3.8.1",
     "rollup-plugin-visualizer": "^7.0.1",
     "web-vitals": "^5.1.0"
diff --git a/frontend/src/App.jsx b/frontend/src/App.jsx
index 5faec365..51ca5a1d 100644
--- a/frontend/src/App.jsx
+++ b/frontend/src/App.jsx
@@ -53,6 +53,7 @@ function App() {
   const { canInstall, install, updateAvailable, applyUpdate } = usePWA();
   const { queue: queueOffline, pendingCount } = useOfflineQueue();
   const { theme, isDark, toggleTheme } = useTheme();
+  useRTL();
   const prefersReduced = useReducedMotion();
   const v = makeVariants(prefersReduced);
   const tap = tapScale(prefersReduced);
@@ -212,6 +213,7 @@ function App() {
           >
             {isDark ? '☀️ Light' : '🌙 Dark'}
           </button>
+          <LanguageSelector />
           {canInstall && (
             <button type="button" className="pwa-install-btn" onClick={install} title="Install app">
               ⬇ Install
diff --git a/frontend/src/components/LanguageSelector.jsx b/frontend/src/components/LanguageSelector.jsx
new file mode 100644
index 00000000..04545517
--- /dev/null
+++ b/frontend/src/components/LanguageSelector.jsx
@@ -0,0 +1,31 @@
+import { useTranslation } from 'react-i18next';
+import { SUPPORTED_LANGUAGES, RTL_LANGUAGES } from '../i18n';
+
+/**
+ * LanguageSelector — dropdown to switch the active language.
+ * Automatically updates <html dir> and <html lang> on change.
+ */
+export function LanguageSelector({ className = '' }) {
+  const { i18n, t } = useTranslation();
+
+  const handleChange = (e) => {
+    const lang = e.target.value;
+    i18n.changeLanguage(lang);
+    document.documentElement.lang = lang;
+    document.documentElement.dir = RTL_LANGUAGES.has(lang) ? 'rtl' : 'ltr';
+  };
+
+  return (
+    <select
+      className={`lang-selector ${className}`}
+      value={i18n.language?.split('-')[0] ?? 'en'}
+      onChange={handleChange}
+      aria-label={t('language.select')}
+      title={t('language.select')}
+    >
+      {SUPPORTED_LANGUAGES.map(({ code, name }) => (
+        <option key={code} value={code}>{name}</option>
+      ))}
+    </select>
+  );
+}
diff --git a/frontend/src/hooks/useRTL.js b/frontend/src/hooks/useRTL.js
new file mode 100644
index 00000000..7da53d5d
--- /dev/null
+++ b/frontend/src/hooks/useRTL.js
@@ -0,0 +1,17 @@
+import { useEffect } from 'react';
+import { useTranslation } from 'react-i18next';
+import { RTL_LANGUAGES } from '../i18n';
+
+/**
+ * Syncs <html dir> and <html lang> whenever the active language changes.
+ * Mount once near the app root (inside I18nextProvider).
+ */
+export function useRTL() {
+  const { i18n } = useTranslation();
+
+  useEffect(() => {
+    const lang = i18n.language?.split('-')[0] ?? 'en';
+    document.documentElement.lang = lang;
+    document.documentElement.dir = RTL_LANGUAGES.has(lang) ? 'rtl' : 'ltr';
+  }, [i18n.language]);
+}
diff --git a/frontend/src/i18n/formatters.js b/frontend/src/i18n/formatters.js
new file mode 100644
index 00000000..f714aa15
--- /dev/null
+++ b/frontend/src/i18n/formatters.js
@@ -0,0 +1,104 @@
+/**
+ * Locale-aware formatting utilities.
+ * All functions accept an optional `locale` parameter (BCP 47 tag).
+ * When omitted they fall back to the current i18n language or browser default.
+ */
+
+import i18n from './index';
+
+function currentLocale() {
+  return i18n.language || navigator.language || 'en';
+}
+
+/**
+ * Format a number for the current locale.
+ * @param {number} value
+ * @param {Intl.NumberFormatOptions} [options]
+ * @param {string} [locale]
+ */
+export function formatNumber(value, options = {}, locale = currentLocale()) {
+  return new Intl.NumberFormat(locale, options).format(value);
+}
+
+/**
+ * Format a currency amount.
+ * @param {number} amount
+ * @param {string} currency  ISO 4217 code, e.g. 'USD', 'EUR'
+ * @param {string} [locale]
+ */
+export function formatCurrency(amount, currency, locale = currentLocale()) {
+  return new Intl.NumberFormat(locale, {
+    style: 'currency',
+    currency,
+    minimumFractionDigits: 2,
+    maximumFractionDigits: 7,
+  }).format(amount);
+}
+
+/**
+ * Format a date/time value.
+ * @param {Date|number|string} value
+ * @param {Intl.DateTimeFormatOptions} [options]
+ * @param {string} [locale]
+ */
+export function formatDate(value, options = { dateStyle: 'medium' }, locale = currentLocale()) {
+  return new Intl.DateTimeFormat(locale, options).format(new Date(value));
+}
+
+/**
+ * Format a date+time.
+ * @param {Date|number|string} value
+ * @param {string} [locale]
+ */
+export function formatDateTime(value, locale = currentLocale()) {
+  return formatDate(value, { dateStyle: 'medium', timeStyle: 'short' }, locale);
+}
+
+/**
+ * Format a relative time (e.g. "3 minutes ago").
+ * @param {Date|number} value  Past or future date
+ * @param {string} [locale]
+ */
+export function formatRelativeTime(value, locale = currentLocale()) {
+  const diffMs = new Date(value) - Date.now();
+  const diffSec = Math.round(diffMs / 1000);
+  const rtf = new Intl.RelativeTimeFormat(locale, { numeric: 'auto' });
+
+  const thresholds = [
+    [60, 'second', 1],
+    [3600, 'minute', 60],
+    [86400, 'hour', 3600],
+    [Infinity, 'day', 86400],
+  ];
+
+  for (const [limit, unit, divisor] of thresholds) {
+    if (Math.abs(diffSec) < limit) {
+      return rtf.format(Math.round(diffSec / divisor), unit);
+    }
+  }
+}
+
+/**
+ * Map a locale code to its preferred currency code.
+ * Falls back to USD for unknown locales.
+ */
+const LOCALE_CURRENCY_MAP = {
+  en: 'USD', 'en-GB': 'GBP', 'en-AU': 'AUD', 'en-CA': 'CAD',
+  ar: 'SAR', 'ar-AE': 'AED', 'ar-EG': 'EGP',
+  he: 'ILS',
+  fr: 'EUR', 'fr-CH': 'CHF',
+  es: 'EUR', 'es-MX': 'MXN', 'es-AR': 'ARS', 'es-CO': 'COP',
+  zh: 'CNY', 'zh-TW': 'TWD', 'zh-HK': 'HKD',
+  pt: 'EUR', 'pt-BR': 'BRL',
+};
+
+/**
+ * Get the preferred currency code for a locale.
+ * @param {string} [locale]
+ * @returns {string} ISO 4217 currency code
+ */
+export function getLocaleCurrency(locale = currentLocale()) {
+  return LOCALE_CURRENCY_MAP[locale]
+    ?? LOCALE_CURRENCY_MAP[locale.split('-')[0]]
+    ?? 'USD';
+}
diff --git a/frontend/src/i18n/index.js b/frontend/src/i18n/index.js
new file mode 100644
index 00000000..5a8e4008
--- /dev/null
+++ b/frontend/src/i18n/index.js
@@ -0,0 +1,41 @@
+import i18n from 'i18next';
+import { initReactI18next } from 'react-i18next';
+import LanguageDetector from 'i18next-browser-languagedetector';
+
+import en from './locales/en.json';
+import ar from './locales/ar.json';
+import he from './locales/he.json';
+import fr from './locales/fr.json';
+import es from './locales/es.json';
+import zh from './locales/zh.json';
+import pt from './locales/pt.json';
+
+/** Languages that use right-to-left text direction */
+export const RTL_LANGUAGES = new Set(['ar', 'he']);
+
+/** All supported locales with their display metadata */
+export const SUPPORTED_LANGUAGES = [
+  { code: 'en', name: 'English',    dir: 'ltr' },
+  { code: 'ar', name: 'العربية',    dir: 'rtl' },
+  { code: 'he', name: 'עברית',      dir: 'rtl' },
+  { code: 'fr', name: 'Français',   dir: 'ltr' },
+  { code: 'es', name: 'Español',    dir: 'ltr' },
+  { code: 'zh', name: '中文',        dir: 'ltr' },
+  { code: 'pt', name: 'Português',  dir: 'ltr' },
+];
+
+i18n
+  .use(LanguageDetector)
+  .use(initReactI18next)
+  .init({
+    resources: { en, ar, he, fr, es, zh, pt },
+    fallbackLng: 'en',
+    interpolation: { escapeValue: false },
+    detection: {
+      order: ['localStorage', 'navigator'],
+      caches: ['localStorage'],
+      lookupLocalStorage: 'i18n_language',
+    },
+  });
+
+export default i18n;
diff --git a/frontend/src/i18n/locales/ar.json b/frontend/src/i18n/locales/ar.json
new file mode 100644
index 00000000..b9b1a562
--- /dev/null
+++ b/frontend/src/i18n/locales/ar.json
@@ -0,0 +1,82 @@
+{
+  "app": {
+    "title": "منصة التحويلات المالية Stellar",
+    "loading": "جارٍ التحميل…"
+  },
+  "nav": {
+    "switchToLight": "التبديل إلى الوضع الفاتح",
+    "switchToDark": "التبديل إلى الوضع الداكن",
+    "light": "☀️ فاتح",
+    "dark": "🌙 داكن",
+    "install": "⬇ تثبيت",
+    "shortcuts": "اختصارات لوحة المفاتيح (?)"
+  },
+  "account": {
+    "create": "إنشاء حساب",
+    "creating": "جارٍ إنشاء الحساب...",
+    "import": "استيراد حساب",
+    "cancelImport": "إلغاء الاستيراد",
+    "publicKey": "المفتاح العام:",
+    "secretKey": "المفتاح السري:",
+    "copyPublicKey": "نسخ المفتاح العام",
+    "copySecretKey": "نسخ المفتاح السري",
+    "showQR": "🔲 عرض رمز QR",
+    "created": "تم إنشاء الحساب! احفظ مفتاحك السري بأمان.",
+    "imported": "تم استيراد الحساب بنجاح!"
+  },
+  "balance": {
+    "check": "التحقق من الرصيد",
+    "checking": "جارٍ التحقق من الرصيد..."
+  },
+  "payment": {
+    "title": "إرسال دفعة",
+    "recipientPlaceholder": "المفتاح العام للمستلم",
+    "recipientLabel": "المفتاح العام للمستلم",
+    "amountPlaceholder": "المبلغ (XLM)",
+    "amountLabel": "مبلغ الدفع بـ XLM",
+    "send": "إرسال",
+    "sending": "جارٍ إرسال الدفعة...",
+    "clear": "مسح",
+    "clearConfirm": "مسح نموذج الدفع؟",
+    "sent": "تم إرسال الدفعة! الرمز: {{hash}}",
+    "queued": "أنت غير متصل. تم وضع الدفعة في قائمة الانتظار وستتم المزامنة تلقائياً.",
+    "largeWarning": "⚠️ يرجى مراجعة وتأكيد تحذير المعاملة الكبيرة أدناه."
+  },
+  "validation": {
+    "invalidAddress": "تنسيق عنوان Stellar غير صالح (يجب أن يبدأ بـ G ويكون 56 حرفاً)"
+  },
+  "pwa": {
+    "updateAvailable": "يتوفر إصدار جديد.",
+    "updateNow": "تحديث الآن",
+    "queued_one": "{{count}} دفعة في قائمة الانتظار — ستتم المزامنة عند الاتصال.",
+    "queued_other": "{{count}} دفعات في قائمة الانتظار — ستتم المزامنة عند الاتصال."
+  },
+  "shortcuts": {
+    "title": "اختصارات لوحة المفاتيح",
+    "close": "إغلاق",
+    "createAccount": "إنشاء حساب جديد",
+    "copyKey": "نسخ المفتاح (عند تركيز زر النسخ)",
+    "escape": "إغلاق النوافذ",
+    "help": "تبديل هذه المساعدة",
+    "tab": "التنقل بين الحقول",
+    "enter": "إرسال النموذج المحدد"
+  },
+  "network": {
+    "connected": "متصل",
+    "disconnected": "غير متصل",
+    "reconnecting": "جارٍ إعادة الاتصال"
+  },
+  "errors": {
+    "timeout": "انتهت مهلة الطلب. يرجى المحاولة مرة أخرى."
+  },
+  "language": {
+    "select": "اللغة",
+    "en": "English",
+    "ar": "العربية",
+    "he": "עברית",
+    "fr": "Français",
+    "es": "Español",
+    "zh": "中文",
+    "pt": "Português"
+  }
+}
diff --git a/frontend/src/i18n/locales/en.json b/frontend/src/i18n/locales/en.json
new file mode 100644
index 00000000..4e9be352
--- /dev/null
+++ b/frontend/src/i18n/locales/en.json
@@ -0,0 +1,82 @@
+{
+  "app": {
+    "title": "Stellar Remittance Platform",
+    "loading": "Loading…"
+  },
+  "nav": {
+    "switchToLight": "Switch to light mode",
+    "switchToDark": "Switch to dark mode",
+    "light": "☀️ Light",
+    "dark": "🌙 Dark",
+    "install": "⬇ Install",
+    "shortcuts": "Keyboard shortcuts (?)"
+  },
+  "account": {
+    "create": "Create Account",
+    "creating": "Creating account...",
+    "import": "Import Account",
+    "cancelImport": "Cancel Import",
+    "publicKey": "Public Key:",
+    "secretKey": "Secret Key:",
+    "copyPublicKey": "Copy public key",
+    "copySecretKey": "Copy secret key",
+    "showQR": "🔲 Show QR Code",
+    "created": "Account created! Save your secret key securely.",
+    "imported": "Account imported successfully!"
+  },
+  "balance": {
+    "check": "Check Balance",
+    "checking": "Checking balance..."
+  },
+  "payment": {
+    "title": "Send Payment",
+    "recipientPlaceholder": "Recipient Public Key",
+    "recipientLabel": "Recipient public key",
+    "amountPlaceholder": "Amount (XLM)",
+    "amountLabel": "Payment amount in XLM",
+    "send": "Send",
+    "sending": "Sending payment...",
+    "clear": "Clear",
+    "clearConfirm": "Clear the payment form?",
+    "sent": "Payment sent! Hash: {{hash}}",
+    "queued": "You are offline. Payment queued and will sync automatically.",
+    "largeWarning": "⚠️ Please review and confirm the large transaction warning below."
+  },
+  "validation": {
+    "invalidAddress": "Invalid Stellar address format (must start with G and be 56 characters)"
+  },
+  "pwa": {
+    "updateAvailable": "A new version is available.",
+    "updateNow": "Update now",
+    "queued_one": "{{count}} payment queued offline — will sync when back online.",
+    "queued_other": "{{count}} payments queued offline — will sync when back online."
+  },
+  "shortcuts": {
+    "title": "Keyboard Shortcuts",
+    "close": "Close",
+    "createAccount": "Create new account",
+    "copyKey": "Copy key (when copy button focused)",
+    "escape": "Close modals",
+    "help": "Toggle this help",
+    "tab": "Navigate between fields",
+    "enter": "Submit focused form"
+  },
+  "network": {
+    "connected": "connected",
+    "disconnected": "disconnected",
+    "reconnecting": "reconnecting"
+  },
+  "errors": {
+    "timeout": "Request timed out. Please try again."
+  },
+  "language": {
+    "select": "Language",
+    "en": "English",
+    "ar": "العربية",
+    "he": "עברית",
+    "fr": "Français",
+    "es": "Español",
+    "zh": "中文",
+    "pt": "Português"
+  }
+}
diff --git a/frontend/src/i18n/locales/es.json b/frontend/src/i18n/locales/es.json
new file mode 100644
index 00000000..fd772689
--- /dev/null
+++ b/frontend/src/i18n/locales/es.json
@@ -0,0 +1,13 @@
+{
+  "app": { "title": "Plataforma de Remesas Stellar", "loading": "Cargando…" },
+  "nav": { "switchToLight": "Cambiar a modo claro", "switchToDark": "Cambiar a modo oscuro", "light": "☀️ Claro", "dark": "🌙 Oscuro", "install": "⬇ Instalar", "shortcuts": "Atajos de teclado (?)" },
+  "account": { "create": "Crear cuenta", "creating": "Creando cuenta...", "import": "Importar cuenta", "cancelImport": "Cancelar importación", "publicKey": "Clave pública:", "secretKey": "Clave secreta:", "copyPublicKey": "Copiar clave pública", "copySecretKey": "Copiar clave secreta", "showQR": "🔲 Mostrar código QR", "created": "¡Cuenta creada! Guarda tu clave secreta de forma segura.", "imported": "¡Cuenta importada con éxito!" },
+  "balance": { "check": "Verificar saldo", "checking": "Verificando saldo..." },
+  "payment": { "title": "Enviar pago", "recipientPlaceholder": "Clave pública del destinatario", "recipientLabel": "Clave pública del destinatario", "amountPlaceholder": "Monto (XLM)", "amountLabel": "Monto del pago en XLM", "send": "Enviar", "sending": "Enviando pago...", "clear": "Limpiar", "clearConfirm": "¿Limpiar el formulario de pago?", "sent": "¡Pago enviado! Hash: {{hash}}", "queued": "Estás sin conexión. Pago en cola, se sincronizará automáticamente.", "largeWarning": "⚠️ Por favor revisa y confirma la advertencia de transacción grande." },
+  "validation": { "invalidAddress": "Formato de dirección Stellar inválido (debe comenzar con G y tener 56 caracteres)" },
+  "pwa": { "updateAvailable": "Hay una nueva versión disponible.", "updateNow": "Actualizar ahora", "queued_one": "{{count}} pago en cola — se sincronizará en línea.", "queued_other": "{{count}} pagos en cola — se sincronizarán en línea." },
+  "shortcuts": { "title": "Atajos de teclado", "close": "Cerrar", "createAccount": "Crear nueva cuenta", "copyKey": "Copiar clave", "escape": "Cerrar modales", "help": "Mostrar/ocultar ayuda", "tab": "Navegar entre campos", "enter": "Enviar formulario" },
+  "network": { "connected": "conectado", "disconnected": "desconectado", "reconnecting": "reconectando" },
+  "errors": { "timeout": "La solicitud expiró. Por favor intenta de nuevo." },
+  "language": { "select": "Idioma", "en": "English", "ar": "العربية", "he": "עברית", "fr": "Français", "es": "Español", "zh": "中文", "pt": "Português" }
+}
diff --git a/frontend/src/i18n/locales/fr.json b/frontend/src/i18n/locales/fr.json
new file mode 100644
index 00000000..5cfcf5f9
--- /dev/null
+++ b/frontend/src/i18n/locales/fr.json
@@ -0,0 +1,13 @@
+{
+  "app": { "title": "Plateforme de Transfert Stellar", "loading": "Chargement…" },
+  "nav": { "switchToLight": "Passer en mode clair", "switchToDark": "Passer en mode sombre", "light": "☀️ Clair", "dark": "🌙 Sombre", "install": "⬇ Installer", "shortcuts": "Raccourcis clavier (?)" },
+  "account": { "create": "Créer un compte", "creating": "Création du compte...", "import": "Importer un compte", "cancelImport": "Annuler l'importation", "publicKey": "Clé publique :", "secretKey": "Clé secrète :", "copyPublicKey": "Copier la clé publique", "copySecretKey": "Copier la clé secrète", "showQR": "🔲 Afficher le QR Code", "created": "Compte créé ! Sauvegardez votre clé secrète en lieu sûr.", "imported": "Compte importé avec succès !" },
+  "balance": { "check": "Vérifier le solde", "checking": "Vérification du solde..." },
+  "payment": { "title": "Envoyer un paiement", "recipientPlaceholder": "Clé publique du destinataire", "recipientLabel": "Clé publique du destinataire", "amountPlaceholder": "Montant (XLM)", "amountLabel": "Montant du paiement en XLM", "send": "Envoyer", "sending": "Envoi du paiement...", "clear": "Effacer", "clearConfirm": "Effacer le formulaire de paiement ?", "sent": "Paiement envoyé ! Hash : {{hash}}", "queued": "Vous êtes hors ligne. Paiement mis en file d'attente.", "largeWarning": "⚠️ Veuillez examiner et confirmer l'avertissement de grande transaction ci-dessous." },
+  "validation": { "invalidAddress": "Format d'adresse Stellar invalide (doit commencer par G et comporter 56 caractères)" },
+  "pwa": { "updateAvailable": "Une nouvelle version est disponible.", "updateNow": "Mettre à jour", "queued_one": "{{count}} paiement en attente — sera synchronisé en ligne.", "queued_other": "{{count}} paiements en attente — seront synchronisés en ligne." },
+  "shortcuts": { "title": "Raccourcis clavier", "close": "Fermer", "createAccount": "Créer un nouveau compte", "copyKey": "Copier la clé", "escape": "Fermer les modales", "help": "Afficher/masquer cette aide", "tab": "Naviguer entre les champs", "enter": "Soumettre le formulaire" },
+  "network": { "connected": "connecté", "disconnected": "déconnecté", "reconnecting": "reconnexion" },
+  "errors": { "timeout": "La requête a expiré. Veuillez réessayer." },
+  "language": { "select": "Langue", "en": "English", "ar": "العربية", "he": "עברית", "fr": "Français", "es": "Español", "zh": "中文", "pt": "Português" }
+}
diff --git a/frontend/src/i18n/locales/he.json b/frontend/src/i18n/locales/he.json
new file mode 100644
index 00000000..be5a62bb
--- /dev/null
+++ b/frontend/src/i18n/locales/he.json
@@ -0,0 +1,82 @@
+{
+  "app": {
+    "title": "פלטפורמת העברות Stellar",
+    "loading": "טוען…"
+  },
+  "nav": {
+    "switchToLight": "עבור למצב בהיר",
+    "switchToDark": "עבור למצב כהה",
+    "light": "☀️ בהיר",
+    "dark": "🌙 כהה",
+    "install": "⬇ התקן",
+    "shortcuts": "קיצורי מקלדת (?)"
+  },
+  "account": {
+    "create": "צור חשבון",
+    "creating": "יוצר חשבון...",
+    "import": "ייבא חשבון",
+    "cancelImport": "בטל ייבוא",
+    "publicKey": "מפתח ציבורי:",
+    "secretKey": "מפתח סודי:",
+    "copyPublicKey": "העתק מפתח ציבורי",
+    "copySecretKey": "העתק מפתח סודי",
+    "showQR": "🔲 הצג קוד QR",
+    "created": "החשבון נוצר! שמור את המפתח הסודי שלך בבטחה.",
+    "imported": "החשבון יובא בהצלחה!"
+  },
+  "balance": {
+    "check": "בדוק יתרה",
+    "checking": "בודק יתרה..."
+  },
+  "payment": {
+    "title": "שלח תשלום",
+    "recipientPlaceholder": "מפתח ציבורי של הנמען",
+    "recipientLabel": "מפתח ציבורי של הנמען",
+    "amountPlaceholder": "סכום (XLM)",
+    "amountLabel": "סכום התשלום ב-XLM",
+    "send": "שלח",
+    "sending": "שולח תשלום...",
+    "clear": "נקה",
+    "clearConfirm": "לנקות את טופס התשלום?",
+    "sent": "התשלום נשלח! גיבוב: {{hash}}",
+    "queued": "אתה לא מחובר. התשלום נוסף לתור ויסונכרן אוטומטית.",
+    "largeWarning": "⚠️ אנא בדוק ואשר את אזהרת העסקה הגדולה למטה."
+  },
+  "validation": {
+    "invalidAddress": "פורמט כתובת Stellar לא חוקי (חייב להתחיל ב-G ולהיות 56 תווים)"
+  },
+  "pwa": {
+    "updateAvailable": "גרסה חדשה זמינה.",
+    "updateNow": "עדכן עכשיו",
+    "queued_one": "{{count}} תשלום בתור — יסונכרן בעת חיבור.",
+    "queued_other": "{{count}} תשלומים בתור — יסונכרנו בעת חיבור."
+  },
+  "shortcuts": {
+    "title": "קיצורי מקלדת",
+    "close": "סגור",
+    "createAccount": "צור חשבון חדש",
+    "copyKey": "העתק מפתח (כשכפתור ההעתקה ממוקד)",
+    "escape": "סגור חלונות",
+    "help": "הצג/הסתר עזרה זו",
+    "tab": "נווט בין שדות",
+    "enter": "שלח טופס ממוקד"
+  },
+  "network": {
+    "connected": "מחובר",
+    "disconnected": "מנותק",
+    "reconnecting": "מתחבר מחדש"
+  },
+  "errors": {
+    "timeout": "הבקשה פגה. אנא נסה שוב."
+  },
+  "language": {
+    "select": "שפה",
+    "en": "English",
+    "ar": "العربية",
+    "he": "עברית",
+    "fr": "Français",
+    "es": "Español",
+    "zh": "中文",
+    "pt": "Português"
+  }
+}
diff --git a/frontend/src/i18n/locales/pt.json b/frontend/src/i18n/locales/pt.json
new file mode 100644
index 00000000..b8766f37
--- /dev/null
+++ b/frontend/src/i18n/locales/pt.json
@@ -0,0 +1,13 @@
+{
+  "app": { "title": "Plataforma de Remessas Stellar", "loading": "Carregando…" },
+  "nav": { "switchToLight": "Mudar para modo claro", "switchToDark": "Mudar para modo escuro", "light": "☀️ Claro", "dark": "🌙 Escuro", "install": "⬇ Instalar", "shortcuts": "Atalhos de teclado (?)" },
+  "account": { "create": "Criar conta", "creating": "Criando conta...", "import": "Importar conta", "cancelImport": "Cancelar importação", "publicKey": "Chave pública:", "secretKey": "Chave secreta:", "copyPublicKey": "Copiar chave pública", "copySecretKey": "Copiar chave secreta", "showQR": "🔲 Mostrar QR Code", "created": "Conta criada! Salve sua chave secreta com segurança.", "imported": "Conta importada com sucesso!" },
+  "balance": { "check": "Verificar saldo", "checking": "Verificando saldo..." },
+  "payment": { "title": "Enviar pagamento", "recipientPlaceholder": "Chave pública do destinatário", "recipientLabel": "Chave pública do destinatário", "amountPlaceholder": "Valor (XLM)", "amountLabel": "Valor do pagamento em XLM", "send": "Enviar", "sending": "Enviando pagamento...", "clear": "Limpar", "clearConfirm": "Limpar o formulário de pagamento?", "sent": "Pagamento enviado! Hash: {{hash}}", "queued": "Você está offline. Pagamento na fila, será sincronizado automaticamente.", "largeWarning": "⚠️ Por favor revise e confirme o aviso de transação grande abaixo." },
+  "validation": { "invalidAddress": "Formato de endereço Stellar inválido (deve começar com G e ter 56 caracteres)" },
+  "pwa": { "updateAvailable": "Uma nova versão está disponível.", "updateNow": "Atualizar agora", "queued_one": "{{count}} pagamento na fila — será sincronizado online.", "queued_other": "{{count}} pagamentos na fila — serão sincronizados online." },
+  "shortcuts": { "title": "Atalhos de teclado", "close": "Fechar", "createAccount": "Criar nova conta", "copyKey": "Copiar chave", "escape": "Fechar modais", "help": "Mostrar/ocultar ajuda", "tab": "Navegar entre campos", "enter": "Enviar formulário" },
+  "network": { "connected": "conectado", "disconnected": "desconectado", "reconnecting": "reconectando" },
+  "errors": { "timeout": "A solicitação expirou. Por favor tente novamente." },
+  "language": { "select": "Idioma", "en": "English", "ar": "العربية", "he": "עברית", "fr": "Français", "es": "Español", "zh": "中文", "pt": "Português" }
+}
diff --git a/frontend/src/i18n/locales/zh.json b/frontend/src/i18n/locales/zh.json
new file mode 100644
index 00000000..d53d44ba
--- /dev/null
+++ b/frontend/src/i18n/locales/zh.json
@@ -0,0 +1,13 @@
+{
+  "app": { "title": "Stellar 汇款平台", "loading": "加载中…" },
+  "nav": { "switchToLight": "切换到浅色模式", "switchToDark": "切换到深色模式", "light": "☀️ 浅色", "dark": "🌙 深色", "install": "⬇ 安装", "shortcuts": "键盘快捷键 (?)" },
+  "account": { "create": "创建账户", "creating": "正在创建账户...", "import": "导入账户", "cancelImport": "取消导入", "publicKey": "公钥：", "secretKey": "私钥：", "copyPublicKey": "复制公钥", "copySecretKey": "复制私钥", "showQR": "🔲 显示二维码", "created": "账户已创建！请安全保存您的私钥。", "imported": "账户导入成功！" },
+  "balance": { "check": "查询余额", "checking": "正在查询余额..." },
+  "payment": { "title": "发送付款", "recipientPlaceholder": "收款人公钥", "recipientLabel": "收款人公钥", "amountPlaceholder": "金额 (XLM)", "amountLabel": "XLM付款金额", "send": "发送", "sending": "正在发送付款...", "clear": "清除", "clearConfirm": "清除付款表单？", "sent": "付款已发送！哈希：{{hash}}", "queued": "您处于离线状态。付款已排队，将在联网后自动同步。", "largeWarning": "⚠️ 请查看并确认下方的大额交易警告。" },
+  "validation": { "invalidAddress": "Stellar地址格式无效（必须以G开头且为56个字符）" },
+  "pwa": { "updateAvailable": "有新版本可用。", "updateNow": "立即更新", "queued_one": "{{count}} 笔付款排队中 — 联网后将同步。", "queued_other": "{{count}} 笔付款排队中 — 联网后将同步。" },
+  "shortcuts": { "title": "键盘快捷键", "close": "关闭", "createAccount": "创建新账户", "copyKey": "复制密钥", "escape": "关闭弹窗", "help": "显示/隐藏帮助", "tab": "在字段间导航", "enter": "提交表单" },
+  "network": { "connected": "已连接", "disconnected": "已断开", "reconnecting": "重新连接中" },
+  "errors": { "timeout": "请求超时，请重试。" },
+  "language": { "select": "语言", "en": "English", "ar": "العربية", "he": "עברית", "fr": "Français", "es": "Español", "zh": "中文", "pt": "Português" }
+}
diff --git a/frontend/tests/i18n.test.js b/frontend/tests/i18n.test.js
new file mode 100644
index 00000000..ce991b9d
--- /dev/null
+++ b/frontend/tests/i18n.test.js
@@ -0,0 +1,53 @@
+import { render, screen, fireEvent } from '@testing-library/react';
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { formatNumber, formatCurrency, formatDate, formatRelativeTime, getLocaleCurrency } from '../src/i18n/formatters';
+
+// Mock i18n so formatters don't need the full init
+vi.mock('../src/i18n/index.js', () => ({ default: { language: 'en' } }));
+
+describe('formatNumber', () => {
+  it('formats with locale grouping', () => {
+    expect(formatNumber(1234567, {}, 'en')).toBe('1,234,567');
+    expect(formatNumber(1234567, {}, 'fr')).toBe('1\u202f234\u202f567');
+  });
+});
+
+describe('formatCurrency', () => {
+  it('formats USD', () => {
+    expect(formatCurrency(1234.5, 'USD', 'en')).toContain('1,234.50');
+  });
+
+  it('formats EUR in French locale', () => {
+    const result = formatCurrency(1234.5, 'EUR', 'fr');
+    expect(result).toContain('1');
+    expect(result).toContain('234');
+  });
+});
+
+describe('formatDate', () => {
+  it('returns a non-empty string', () => {
+    const result = formatDate(new Date('2026-01-15'), { dateStyle: 'medium' }, 'en');
+    expect(result).toMatch(/Jan/i);
+  });
+});
+
+describe('formatRelativeTime', () => {
+  it('returns "now" or seconds for very recent time', () => {
+    const result = formatRelativeTime(Date.now() - 5000, 'en');
+    expect(typeof result).toBe('string');
+    expect(result.length).toBeGreaterThan(0);
+  });
+
+  it('returns minutes for ~2 min ago', () => {
+    const result = formatRelativeTime(Date.now() - 2 * 60 * 1000, 'en');
+    expect(result).toMatch(/minute/i);
+  });
+});
+
+describe('getLocaleCurrency', () => {
+  it('returns USD for en', () => expect(getLocaleCurrency('en')).toBe('USD'));
+  it('returns ILS for he', () => expect(getLocaleCurrency('he')).toBe('ILS'));
+  it('returns SAR for ar', () => expect(getLocaleCurrency('ar')).toBe('SAR'));
+  it('returns BRL for pt-BR', () => expect(getLocaleCurrency('pt-BR')).toBe('BRL'));
+  it('falls back to USD for unknown', () => expect(getLocaleCurrency('xx')).toBe('USD'));
+});
diff --git a/package-lock.json b/package-lock.json
index db7e0bef..0de7f917 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -57,9 +57,12 @@
         "@tanstack/react-virtual": "^3.13.23",
         "axios": "^1.7.2",
         "framer-motion": "^12.38.0",
+        "i18next": "^23.11.5",
+        "i18next-browser-languagedetector": "^8.0.0",
         "qrcode": "^1.5.4",
         "react": "^18.3.1",
         "react-dom": "^18.3.1",
+        "react-i18next": "^14.1.2",
         "recharts": "^3.8.1",
         "rollup-plugin-visualizer": "^7.0.1",
         "web-vitals": "^5.1.0"
@@ -1007,7 +1010,6 @@
     },
     "node_modules/@babel/runtime": {
       "version": "7.29.2",
-      "dev": true,
       "license": "MIT",
       "engines": {
         "node": ">=6.9.0"
@@ -6602,6 +6604,39 @@
       ],
       "license": "MIT"
     },
+    "node_modules/@vitest/coverage-v8": {
+      "version": "4.1.1",
+      "resolved": "https://registry.npmjs.org/@vitest/coverage-v8/-/coverage-v8-4.1.1.tgz",
+      "integrity": "sha512-nZ4RWwGCoGOQRMmU/Q9wlUY540RVRxJZ9lxFsFfy0QV7Zmo5VVBhB6Sl9Xa0KIp2iIs3zWfPlo9LcY1iqbpzCw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@bcoe/v8-coverage": "^1.0.2",
+        "@vitest/utils": "4.1.1",
+        "ast-v8-to-istanbul": "^1.0.0",
+        "istanbul-lib-coverage": "^3.2.2",
+        "istanbul-lib-report": "^3.0.1",
+        "istanbul-reports": "^3.2.0",
+        "magicast": "^0.5.2",
+        "obug": "^2.1.1",
+        "std-env": "^4.0.0-rc.1",
+        "tinyrainbow": "^3.0.3"
+      },
+      "funding": {
+        "url": "https://opencollective.com/vitest"
+      },
+      "peerDependencies": {
+        "@vitest/browser": "4.1.1",
+        "vitest": "4.1.1"
+      },
+      "peerDependenciesMeta": {
+        "@vitest/browser": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/@vitest/expect": {
+      "version": "4.1.1",
     "node_modules/baseline-browser-mapping": {
       "version": "2.10.10",
       "dev": true,
@@ -7415,6 +7450,51 @@
         "node": ">= 12"
       }
     },
+    "node_modules/chart.js": {
+      "version": "4.5.1",
+      "resolved": "https://registry.npmjs.org/chart.js/-/chart.js-4.5.1.tgz",
+      "integrity": "sha512-GIjfiT9dbmHRiYi6Nl2yFCq7kkwdkp1W/lp2J99rX0yo9tgJGn3lKQATztIjb5tVtevcBtIdICNWqlq5+E8/Pw==",
+      "license": "MIT",
+      "dependencies": {
+        "@kurkle/color": "^0.3.0"
+      },
+      "engines": {
+        "pnpm": ">=8"
+      }
+    },
+    "node_modules/chokidar": {
+      "version": "4.0.3",
+      "resolved": "https://registry.npmjs.org/chokidar/-/chokidar-4.0.3.tgz",
+      "integrity": "sha512-Qgzu8kfBvo+cA4962jnP1KkS6Dop5NS6g7R5LFYJr4b8Ub94PPQXUksCw9PvXoeXPRRddRNC5C1JQUR2SMGtnA==",
+      "license": "MIT",
+      "dependencies": {
+        "readdirp": "^4.0.1"
+      },
+      "engines": {
+        "node": ">= 14.16.0"
+      },
+      "funding": {
+        "url": "https://paulmillr.com/funding/"
+      }
+    },
+    "node_modules/citty": {
+      "version": "0.1.6",
+      "resolved": "https://registry.npmjs.org/citty/-/citty-0.1.6.tgz",
+      "integrity": "sha512-tskPPKEs8D2KPafUypv2gxwJP8h/OaJmC82QQGGDQcHvXX43xF2VDACcJVmZ0EuSxkpO9Kc4MlrA3q0+FG58AQ==",
+      "license": "MIT",
+      "dependencies": {
+        "consola": "^3.2.3"
+      }
+    },
+    "node_modules/cliui": {
+      "version": "8.0.1",
+      "dev": true,
+      "license": "ISC",
+      "dependencies": {
+        "string-width": "^4.2.0",
+        "strip-ansi": "^6.0.1",
+        "wrap-ansi": "^7.0.0"
+      },
     "node_modules/deepmerge-ts": {
       "version": "7.1.5",
       "resolved": "https://registry.npmjs.org/deepmerge-ts/-/deepmerge-ts-7.1.5.tgz",
@@ -9350,6 +9430,15 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/html-parse-stringify": {
+      "version": "3.0.1",
+      "resolved": "https://registry.npmjs.org/html-parse-stringify/-/html-parse-stringify-3.0.1.tgz",
+      "integrity": "sha512-KknJ50kTInJ7qIScF3jeaFRpMpE8/lfiTdzf/twXyPBLAGrLRTmkz3AdTnKeh40X8k9L2fdYwEp/42WGXIRGcg==",
+      "license": "MIT",
+      "dependencies": {
+        "void-elements": "3.1.0"
+      }
+    },
     "node_modules/http-errors": {
       "version": "2.0.1",
       "license": "MIT",
@@ -12024,6 +12113,28 @@
         "react": "^18.3.1"
       }
     },
+    "node_modules/react-i18next": {
+      "version": "14.1.3",
+      "resolved": "https://registry.npmjs.org/react-i18next/-/react-i18next-14.1.3.tgz",
+      "integrity": "sha512-wZnpfunU6UIAiJ+bxwOiTmBOAaB14ha97MjOEnLGac2RJ+h/maIYXZuTHlmyqQVX1UVHmU1YDTQ5vxLmwfXTjw==",
+      "license": "MIT",
+      "dependencies": {
+        "@babel/runtime": "^7.23.9",
+        "html-parse-stringify": "^3.0.1"
+      },
+      "peerDependencies": {
+        "i18next": ">= 23.2.3",
+        "react": ">= 16.8.0"
+      },
+      "peerDependenciesMeta": {
+        "react-dom": {
+          "optional": true
+        },
+        "react-native": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/react-is": {
       "version": "17.0.2",
       "license": "MIT",
@@ -13763,6 +13874,15 @@
         }
       }
     },
+    "node_modules/void-elements": {
+      "version": "3.1.0",
+      "resolved": "https://registry.npmjs.org/void-elements/-/void-elements-3.1.0.tgz",
+      "integrity": "sha512-Dhxzh5HZuiHQhbvTW9AMetFfBHDMYpo23Uo9btPXgdYP+3T5S+p+jgNy7spra+veYhBP2dCSgxR/i2Y02h5/6w==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=0.10.0"
+      }
+    },
     "node_modules/w3c-xmlserializer": {
       "version": "5.0.0",
       "dev": true,
