Fix runtime default locale resolution

lib/locale.ts

@@ -1,21 +1,23 @@
-import { routing } from "../i18n/routing";
+import { appLocales } from "../i18n/routing";
 
-export type AppLocale = (typeof routing.locales)[number];
+export type AppLocale = (typeof appLocales)[number];
 
-export function resolveLocale(locale: string): AppLocale {
-  if (locale === "en" || locale === "ar") {
-    return locale;
-  }
+export const FALLBACK_LOCALE: AppLocale = "de";
 
-  return routing.defaultLocale;
+export function isSupportedLocale(locale: string | undefined | null): locale is AppLocale {
+  return locale === "de" || locale === "en" || locale === "ar";
+}
+
+export function resolveLocale(locale: string | undefined | null, fallbackLocale: AppLocale): AppLocale {
+  return isSupportedLocale(locale) ? locale : fallbackLocale;
 }
 
 export function getDirection(locale: string): "ltr" | "rtl" {
-  return resolveLocale(locale) === "ar" ? "rtl" : "ltr";
+  return locale === "ar" ? "rtl" : "ltr";
 }
 
 export function stripLocalePrefix(pathname: string): string {
-  for (const locale of routing.locales) {
+  for (const locale of appLocales) {
     if (pathname === `/${locale}`) {
       return "/";
     }
@@ -31,7 +33,7 @@ export function stripLocalePrefix(pathname: string): string {
 export function getLocalizedPath(
   locale: string,
   pathname = "/",
-  defaultLocale: AppLocale = routing.defaultLocale,
+  defaultLocale: AppLocale,
 ): string {
   return getLocalizedPathWithDefault(locale, pathname, defaultLocale);
 }
@@ -39,9 +41,9 @@ export function getLocalizedPath(
 export function getLocalizedPathWithDefault(
   locale: string,
   pathname = "/",
-  defaultLocale: AppLocale = routing.defaultLocale,
+  defaultLocale: AppLocale,
 ): string {
-  const localeKey = resolveLocale(locale);
+  const localeKey = resolveLocale(locale, defaultLocale);
   const normalizedPath = pathname === "" ? "/" : pathname;
   const strippedPath = stripLocalePrefix(normalizedPath);