feat: i18n 개선 및 userfront 로그인/로케일 보완

adminfront/src/components/layout/AppLayout.tsx

@@ -13,6 +13,7 @@ import {
 import { useEffect, useState } from "react";
 import { NavLink, Outlet } from "react-router-dom";
 import { t } from "../../lib/i18n";
+import LanguageSelector from "../common/LanguageSelector";
 import RoleSwitcher from "./RoleSwitcher";
 
 const navItems = [
@@ -132,6 +133,7 @@ function AppLayout() {
               </span>
             </div>
             <div className="flex items-center gap-2 text-sm">
+              <LanguageSelector />
               <button
                 type="button"
                 onClick={toggleTheme}