diff --git a/src/boot/lang.js b/src/boot/lang.js
index 3b50639..76820fe 100644
--- a/src/boot/lang.js
+++ b/src/boot/lang.js
@@ -24,10 +24,27 @@ for (const path in modules) {
   messages[locale] = parsed;
 }
 
+function resolveLocale(desiredLocale) {
+  if (messages[desiredLocale]) return desiredLocale;
+
+  const baseLang = desiredLocale.split('-')[0];
+  // exact base match (e.g. en)
+  if (messages[baseLang]) return baseLang;
+
+  // first locale starting with that base (e.g. en-US, en-GB)
+  const partialMatch = Object.keys(messages).find((l) => l.startsWith(baseLang));
+  if (partialMatch) return partialMatch;
+
+  // fallback to English or the first available
+  return messages['en'] ? 'en' : Object.keys(messages)[0];
+}
+
+const selectedLocale = resolveLocale(savedLang || systemLocale);
+
 const i18n = createI18n({
   legacy: false, // Composition API mode
-  locale: savedLang || systemLocale,
-  fallbackLocale: systemLocale,
+  locale: selectedLocale,
+  fallbackLocale: resolveLocale(selectedLocale),
   messages,
 });