Fix /share and cleanup and reorganize frontend locale loading (#25240)

app/javascript/mastodon/locales/global_locale.ts

@@ -0,0 +1,22 @@
+export interface LocaleData {
+  locale: string;
+  messages: Record<string, string>;
+}
+
+let loadedLocale: LocaleData;
+
+export function setLocale(locale: LocaleData) {
+  loadedLocale = locale;
+}
+
+export function getLocale() {
+  if (!loadedLocale && process.env.NODE_ENV === 'development') {
+    throw new Error('getLocale() called before any locale has been set');
+  }
+
+  return loadedLocale;
+}
+
+export function isLocaleLoaded() {
+  return !!loadedLocale;
+}