feat(admin-i18n): add cookie-based locale runtime and switcher baseline

apps/admin/src/i18n/server.ts

@@ -0,0 +1,20 @@
+import { type AppLocale, defaultLocale, isAppLocale } from "@cms/i18n"
+import { cookies } from "next/headers"
+
+import type { AdminMessages } from "./messages"
+import { ADMIN_LOCALE_COOKIE } from "./shared"
+
+export async function resolveAdminLocale(): Promise<AppLocale> {
+  const cookieStore = await cookies()
+  const value = cookieStore.get(ADMIN_LOCALE_COOKIE)?.value
+
+  if (value && isAppLocale(value)) {
+    return value
+  }
+
+  return defaultLocale
+}
+
+export async function getAdminMessages(locale: AppLocale): Promise<AdminMessages> {
+  return (await import(`../messages/${locale}.json`)).default as AdminMessages
+}