fix(middleware): handle invalid locale values in Accept-Language header

Added error handling to prevent middleware crashes when browsers send
invalid locale codes. Filters out malformed locale values before passing
to Intl.getCanonicalLocales, with fallback to default locale if all
values are invalid.

Fixes: RangeError: Incorrect locale information provided

src/middleware.ts

@@ -14,8 +14,28 @@ function getLocale(request: NextRequest): string {
     negotiatorHeaders[key] = value;
   });
 
+  try {
     const languages = new Negotiator({ headers: negotiatorHeaders }).languages();
-  return match(languages, i18n.locales, i18n.defaultLocale);
+    // Filter out invalid locale values that would cause Intl.getCanonicalLocales to fail
+    const validLanguages = languages.filter((lang) => {
+      try {
+        Intl.getCanonicalLocales(lang);
+        return true;
+      } catch {
+        return false;
+      }
+    });
+
+    if (validLanguages.length === 0) {
+      return i18n.defaultLocale;
+    }
+
+    return match(validLanguages, i18n.locales, i18n.defaultLocale);
+  } catch (error) {
+    // Fallback to default locale if locale negotiation fails
+    console.error('Locale negotiation error:', error);
+    return i18n.defaultLocale;
+  }
 }
 
 export function middleware(request: NextRequest) {