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

apps/admin/src/i18n/messages.ts

@@ -0,0 +1,27 @@
+import type enMessages from "../messages/en.json"
+
+export type AdminMessages = typeof enMessages
+
+function resolveNestedValue(source: unknown, key: string): unknown {
+  let current: unknown = source
+
+  for (const segment of key.split(".")) {
+    if (!current || typeof current !== "object") {
+      return null
+    }
+
+    current = (current as Record<string, unknown>)[segment]
+  }
+
+  return current
+}
+
+export function translateMessage(messages: AdminMessages, key: string, fallback?: string): string {
+  const resolved = resolveNestedValue(messages, key)
+
+  if (typeof resolved === "string") {
+    return resolved
+  }
+
+  return fallback ?? key
+}