@elsoul/fresh-i18n

@elsoul/fresh-i18n is an efficient and adaptable internationalization (i18n) plugin designed specifically for Deno's Fresh v2 framework. It enables easy language management within your Fresh app, providing JSON-based translations, automatic locale detection, and optimized data loading for an edge-native experience.

Features

  • Automatic Locale Detection: Seamlessly detects the user's language from URL parameters, defaulting to a specified language when needed.
  • Modular Translation Loading: Organize translations by namespaces for structured, optimized JSON loading.
  • Intuitive API: Fetch translations via useTranslation() and access or switch locales with useLocale().
  • Optimized for Deno Edge: Designed to work efficiently in edge environments, leveraging Deno's performance.
  • Dynamic Language Switching: Allows for real-time language changes within components without a page reload.

Installation

Install via JSR

import { i18nPlugin } from 'jsr:@elsoul/fresh-i18n'

Install via Deno Land

import { i18nPlugin } from 'https://deno.land/x/fresh_i18n/mod.ts'

Usage

Step 1: Register the Plugin

In your main.ts, initialize the plugin with available languages, default locale, and translation directory. This setup automatically detects the preferred locale based on the URL.

import { App, fsRoutes, staticFiles, trailingSlashes } from 'fresh'
import { i18nPlugin } from 'fresh-i18n'
import type { ExtendedState } from '@/utils/state.ts'

export const app = new App<ExtendedState>({
  root: import.meta.url,
})
  .use(staticFiles())
  .use(trailingSlashes('never'))
  .use(i18nPlugin({
    languages: ['en', 'ja'],
    defaultLanguage: 'en',
    localesDir: './locales',
  }))

await fsRoutes(app, {
  loadIsland: (path) => import(`./islands/${path}`),
  loadRoute: (path) => import(`./routes/${path}`),
})

if (import.meta.main) {
  await app.listen()
}

Define an Extended State with TranslationState

If you are managing additional global state in your Fresh app, such as metadata or theme settings, you can extend TranslationState to include your own properties. This extended state can then be used across your app, with translation data (t) accessible directly in request handlers, enabling Server-Side Rendering (SSR) with fully localized content.

Example

In the following example, TranslationState from @elsoul/fresh-i18n is combined with a custom State interface to create ExtendedState. This ExtendedState includes both translation data and other application-specific properties, making it convenient for global state management.

ExtendedState can then be used in request handlers to access translation data directly via ctx.state.t, enabling SSR with localized data.

import { createDefine } from 'fresh'
import type { TranslationState } from 'fresh-i18n'

interface State {
  title?: string
  theme?: string
  description?: string
  ogImage?: string
  noIndex?: boolean
}

export type ExtendedState = State & TranslationState

export const define = createDefine<ExtendedState>()

Step 2: Create Locale JSON Files

Inside the locales directory, create subfolders for each locale and organize translation keys in namespace files. These files are loaded dynamically based on the URL structure.

For example, if the URL is https://example.com/en/company/profile, the plugin will load the following files (if they exist):

  • ./locales/en/common.json (always loaded as the base translation)
  • ./locales/en/metadata.json (always loaded as the base translation)
  • ./locales/en/error.json (always loaded as the base translation)
  • ./locales/en/company.json
  • ./locales/en/profile.json

Each of these files corresponds to a "namespace" in the translation data. If a file does not exist, it is skipped without an error, ensuring flexibility.

Example: locales/en/common.json

{
  "welcome": "Welcome",
  "title": "Home"
}

Example: locales/ja/common.json

{
  "welcome": "ようこそ",
  "title": "ホーム"
}

Step 3: Use Translations in Routes

import { define } from '@/utils/state.ts'

export const handler = define.handlers({
  GET(ctx) {
    console.log('ctx', ctx.state.translationData) // Access translation data directly
    return page()
  },
})

export default define.page<typeof handler>(function Home(props) {
  console.log('props', props.state.t('common.title')) // Access translation data using getTranslation function via props
  return (
    <div>
    </div>
  )
})

Step 4: Use Translation in Islands

You need to share ctx.state data with islands.

import type { PageProps } from 'fresh'
import StateShareLayer from '@/islands/layouts/StateShareLayer.tsx'
import type { ExtendedState } from '@/utils/state.ts'

export default function RootLayout(
  { Component, state }: PageProps,
) {
  return (
    <>
      <StateShareLayer state={state as ExtendedState} />
      <Component />
    </>
  )
}
import { type ExtendedState } from '@/utils/state.ts'
import { atom, useAtom } from 'fresh-atom'
import { useEffect } from 'preact/hooks'

type Props = {
  state: ExtendedState
}

export const stateAtom = atom<ExtendedState>({
  title: '',
  theme: 'dark',
  description: '',
  ogImage: '',
  noIndex: false,
  locale: 'en',
  t: {},
  path: '/',
})

export default function StateShareLayer({ state }: Props) {
  const [, setState] = useAtom(stateAtom)

  useEffect(() => {
    setState(state)
  }, [state])

  return null
}

Useful hooks

You can create useful hooks to access translation data on islands.

import { useAtom } from 'fresh-atom'
import { stateAtom } from '@/islands/layouts/StateShareLayer.tsx'

export function useTranslation() {
  const [state] = useAtom(stateAtom)

  /**
   * Translates a key string like 'common.title' or 'common.titlerow.title.example'
   * by traversing the nested structure of `state.t`.
   *
   * @param key - The translation key in dot notation (e.g., 'common.title').
   * @returns The translated string, or an empty string if the key is not found.
   */
  const t = (key: string): string => {
    const keys = key.split('.')
    let result: Record<string, unknown> | string = state.t

    for (const k of keys) {
      if (typeof result === 'object' && result !== null && k in result) {
        result = result[k] as Record<string, unknown> | string
      } else {
        return '' // Key not found, return empty string or default text
      }
    }

    return typeof result === 'string' ? result : '' // Return the result if it's a string
  }

  return { t }
}
import { useAtom } from 'fresh-atom'
import { stateAtom } from '@/islands/layouts/StateShareLayer.tsx'

export function usePathname() {
  const [state] = useAtom(stateAtom)
  return state.path
}
import { useAtom } from 'fresh-atom'
import { stateAtom } from '@/islands/layouts/StateShareLayer.tsx'

export function useLocale() {
  const [state, setState] = useAtom(stateAtom)

  /**
   * Sets a new locale, updates the global state, and redirects
   * to the new locale's URL path to update page content.
   *
   * @param locale - The new locale string (e.g., 'en', 'ja').
   */
  const setLocale = (locale: string) => {
    setState((prevState) => ({ ...prevState, locale }))

    const newPath = `/${locale}${state.path}`
    globalThis.location.href = newPath
  }

  return { locale: state.locale, setLocale }
}
Usage
import { useTranslation } from '@/hooks/i18n/useTranslation.ts'
import { usePathname } from '@/hooks/i18n/usePathname.ts'
import { useLocale } from '@/hooks/i18n/useLocale.ts'

export default function IslandsComponent() {
  const { t } = useTranslation()
  const path = usePathname()
  const { locale } = useLocale()

  console.log('path', path)
  console.log('locale', locale)
  return (
    <div>
      {t('common.title')} // Home or ホーム
    </div>
  )
}

Contributing

Contributions are welcome! Please submit any issues or pull requests via GitHub.

License

This package is open-source, available under the Apache-2.0 License.