Modify language identification in locale handling

The update changes the way locales are checked against the list of accepted languages. Now, instead the full locale, only the language segment is considered when determining if the locale is accepted. Additionally, a check in 'getPreferredLanguageFromBrowser' was added to ensure 'acceptLanguage' is not undefined before attempting to parse it.

packages/i18n/src/i18n.server.ts

@@ -73,9 +73,15 @@ export function parseAcceptLanguageHeader(
       // Ignore wildcard '*' if 'ignoreWildcard' is true
       if (locale === '*' && ignoreWildcard) return [];
 
+      const languageSegment = locale.split('-')[0];
+
+      if (!languageSegment) return [];
+
       // Return the locale if it's included in the accepted languages
       try {
-        return acceptedLanguages.includes(locale) ? [locale] : [];
+        return acceptedLanguages.includes(languageSegment)
+          ? [languageSegment]
+          : [];
       } catch {
         return [];
       }