feat(i18n): 국제화 인프라 도입 및 Vuetify 동기화, SideMenu 기본 텍스트 1차 치환

src/i18n/index.js

@@ -0,0 +1,43 @@
+import Vue from 'vue'
+import VueI18n from 'vue-i18n'
+import ko from '@/locales/ko.json'
+import en from '@/locales/en.json'
+import ja from '@/locales/ja.json'
+
+Vue.use(VueI18n)
+
+function detectLocale() {
+  try {
+    const saved = localStorage.getItem('locale')
+    if (saved) return saved
+  } catch (e) {
+    // ignore
+  }
+
+  const list = (navigator.languages && navigator.languages.length
+    ? navigator.languages
+    : [navigator.language || 'en'])
+    .map(l => String(l).toLowerCase())
+
+  for (const l of list) {
+    if (l.startsWith('ko')) return 'ko'
+    if (l.startsWith('ja')) return 'ja'
+    if (l.startsWith('en')) return 'en'
+  }
+  return 'en' // 매칭 실패 시 기본값
+}
+
+const i18n = new VueI18n({
+  locale: detectLocale(),
+  fallbackLocale: 'en',
+  messages: { ko, en, ja },
+  silentTranslationWarn: process.env.NODE_ENV === 'production',
+  missing(locale, key) {
+    if (process.env.NODE_ENV !== 'production') {
+      // eslint-disable-next-line no-console
+      console.warn(`[i18n missing] ${locale}: ${key}`)
+    }
+  }
+})
+
+export default i18n