## Introduction Vue i18n makes it easy to add translations in Vue templates with the `$t()` function. But what about translating text in JavaScript files, Vuex/Pinia stores, or utility functions? This guide shows you how to use Vue i18n translations anywhere in your Vue 3 application, including outside of Vue components. ## Prerequisites - Vue 3 project with vue-i18n installed - Basic understanding of Vue Composition API - Familiarity with i18n concepts ## Basic Setup Recap First, let's ensure your i18n setup supports JavaScript usage: ```javascript // src/i18n/index.js import { createI18n } from 'vue-i18n'; const messages = { en: { greeting: 'Hello, {name}!', errors: { required: 'This field is required', email: 'Please enter a valid email' } }, de: { greeting: 'Hallo, {name}!', errors: { required: 'Dieses Feld ist erforderlich', email: 'Bitte geben Sie eine gültige E-Mail ein' } } }; export const i18n = createI18n({ legacy: false, // Use Composition API mode locale: 'en', fallbackLocale: 'en', messages }); export default i18n; ``` ## Method 1: Using useI18n() Composable The recommended way to access translations in Vue 3 components: ```vue ``` ## Method 2: Global i18n Instance For use outside Vue components (stores, utilities, etc.): ```javascript // src/utils/notifications.js import { i18n } from '@/i18n'; export function showSuccessNotification(key, params = {}) { const message = i18n.global.t(key, params); // Show notification with translated message toast.success(message); } export function showErrorNotification(errorKey) { const message = i18n.global.t(`errors.${errorKey}`); toast.error(message); } ``` ### Using in Pinia Stores ```javascript // src/stores/user.js import { defineStore } from 'pinia'; import { i18n } from '@/i18n'; export const useUserStore = defineStore('user', { state: () => ({ user: null, error: null }), actions: { async login(credentials) { try { const response = await api.login(credentials); this.user = response.data; // Translated success message const message = i18n.global.t('auth.loginSuccess'); toast.success(message); } catch (error) { // Translated error message this.error = i18n.global.t('auth.loginFailed'); throw error; } }, async logout() { this.user = null; const message = i18n.global.t('auth.logoutSuccess'); toast.info(message); } } }); ``` ### Using in Vuex Stores ```javascript // src/store/modules/auth.js import { i18n } from '@/i18n'; export default { namespaced: true, actions: { async login({ commit }, credentials) { try { const user = await api.login(credentials); commit('SET_USER', user); return { success: true, message: i18n.global.t('auth.welcome', { name: user.name }) }; } catch (error) { return { success: false, message: i18n.global.t('auth.error') }; } } } }; ``` ## Method 3: Creating a Translation Helper For cleaner code, create a helper function: ```javascript // src/utils/translate.js import { i18n } from '@/i18n'; /** * Translate a key outside of Vue components * @param {string} key - Translation key * @param {object} params - Interpolation parameters * @returns {string} Translated string */ export function translate(key, params = {}) { return i18n.global.t(key, params); } // Shorthand alias export const $t = translate; // For plural translations export function translatePlural(key, count, params = {}) { return i18n.global.t(key, { count, ...params }); } ``` Usage: ```javascript // src/services/validation.js import { $t } from '@/utils/translate'; export const validationRules = { required: (value) => !!value || $t('errors.required'), email: (value) => { const pattern = /^[^\s@]+@[^\s@]+\.[^\s@]+$/; return pattern.test(value) || $t('errors.email'); }, minLength: (min) => (value) => { return value.length >= min || $t('errors.minLength', { min }); }, maxLength: (max) => (value) => { return value.length <= max || $t('errors.maxLength', { max }); } }; ``` ## Method 4: Reactive Translations with Computed When you need translations to update reactively: ```javascript // src/composables/useTranslatedOptions.js import { computed } from 'vue'; import { useI18n } from 'vue-i18n'; export function useTranslatedOptions() { const { t } = useI18n(); const statusOptions = computed(() => [ { value: 'active', label: t('status.active') }, { value: 'pending', label: t('status.pending') }, { value: 'inactive', label: t('status.inactive') } ]); const priorityOptions = computed(() => [ { value: 'high', label: t('priority.high') }, { value: 'medium', label: t('priority.medium') }, { value: 'low', label: t('priority.low') } ]); return { statusOptions, priorityOptions }; } ``` Usage in component: ```vue ``` ## Method 5: Translation in Route Guards ```javascript // src/router/index.js import { createRouter } from 'vue-router'; import { i18n } from '@/i18n'; const router = createRouter({ // ... routes }); router.beforeEach((to, from, next) => { // Set page title with translation const title = to.meta.titleKey ? i18n.global.t(to.meta.titleKey) : 'My App'; document.title = title; // Check authentication with translated message if (to.meta.requiresAuth && !isAuthenticated()) { toast.error(i18n.global.t('auth.loginRequired')); next('/login'); } else { next(); } }); export default router; ``` ## Method 6: API Error Handling ```javascript // src/services/api.js import axios from 'axios'; import { i18n } from '@/i18n'; const api = axios.create({ baseURL: '/api' }); api.interceptors.response.use( (response) => response, (error) => { const status = error.response?.status; let message; switch (status) { case 400: message = i18n.global.t('errors.badRequest'); break; case 401: message = i18n.global.t('errors.unauthorized'); break; case 403: message = i18n.global.t('errors.forbidden'); break; case 404: message = i18n.global.t('errors.notFound'); break; case 500: message = i18n.global.t('errors.serverError'); break; default: message = i18n.global.t('errors.unknown'); } toast.error(message); return Promise.reject(error); } ); export default api; ``` ## Best Practices ### 1. Always Export i18n Instance ```javascript // i18n/index.js export const i18n = createI18n({ ... }); export default i18n; ``` ### 2. Use Composition API Mode ```javascript createI18n({ legacy: false, // Required for useI18n() // ... }); ``` ### 3. Create Type-Safe Helpers (TypeScript) ```typescript // src/utils/translate.ts import { i18n } from '@/i18n'; import type { TranslateResult } from 'vue-i18n'; type TranslationKey = keyof typeof import('@/i18n/locales/en.json'); export function translate( key: TranslationKey, params?: Record ): TranslateResult { return i18n.global.t(key, params ?? {}); } ``` ### 4. Handle Async Loading ```javascript // For lazy-loaded translations import { i18n } from '@/i18n'; export async function loadLocaleMessages(locale) { const messages = await import(`@/i18n/locales/${locale}.json`); i18n.global.setLocaleMessage(locale, messages.default); return messages; } // Usage async function changeLanguage(locale) { await loadLocaleMessages(locale); i18n.global.locale.value = locale; } ``` ## Common Issues and Solutions ### Issue 1: t() Returns Key Instead of Translation **Problem:** Getting the key back instead of translated text. **Solutions:** ```javascript // Check if messages are loaded console.log(i18n.global.messages.value); // Ensure correct key path i18n.global.t('errors.required'); // Not t('required') // Check locale is set console.log(i18n.global.locale.value); ``` ### Issue 2: Translations Not Reactive **Problem:** Language change doesn't update text. **Solution:** Use computed properties: ```javascript // Wrong - not reactive const message = i18n.global.t('greeting'); // Correct - reactive const message = computed(() => i18n.global.t('greeting')); ``` ### Issue 3: useI18n() Outside Setup **Problem:** `useI18n()` can only be used in setup. **Solution:** Use the global instance: ```javascript // In regular JS files import { i18n } from '@/i18n'; const message = i18n.global.t('key'); // In composables (within component context) import { useI18n } from 'vue-i18n'; const { t } = useI18n(); ``` ### Issue 4: SSR/Nuxt Compatibility **Problem:** Server-side rendering issues. **Solution:** Use the useI18n composable in components: ```javascript // In Nuxt, use the built-in $t export default { setup() { const { $t } = useNuxtApp(); // or const { t } = useI18n(); } }; ``` ## Performance Tips ### Avoid Excessive t() Calls ```javascript // Avoid - multiple calls items.map(item => ({ ...item, statusLabel: i18n.global.t(`status.${item.status}`), typeLabel: i18n.global.t(`type.${item.type}`) })); // Better - batch or memoize const statusLabels = { active: i18n.global.t('status.active'), pending: i18n.global.t('status.pending') }; items.map(item => ({ ...item, statusLabel: statusLabels[item.status] })); ``` ## Conclusion Vue i18n provides flexible ways to use translations in JavaScript: 1. **useI18n()** - Best for Vue components with Composition API 2. **i18n.global.t()** - For stores, utilities, and non-component code 3. **Helper functions** - For cleaner, reusable translation access 4. **Computed properties** - For reactive translations When translating your Vue i18n JSON files, ensure placeholders and ICU format are preserved. [appstoretranslate.com](https://appstoretranslate.com) automatically handles Vue i18n file formats while maintaining all variable syntax. ## Related Resources - [React i18next Placeholder Guide](/blog/react-i18next-placeholder) - [React i18next Trans Component](/blog/react-i18next-trans-component) - [Android i18n JSON Guide](/blog/android-i18n-json-guide) - [Vue i18n Official Documentation](https://vue-i18n.intlify.dev/)