i18n wrapper and Koa middleware for Lad

Usage no npm install needed!

<script type="module">
  import ladjsI18n from 'https://cdn.skypack.dev/@ladjs/i18n';



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i18n wrapper and Koa middleware for Lad

Table of Contents



npm install @ladjs/i18n


yarn add @ladjs/i18n


const I18N = require('@ladjs/i18n');
const phrases = { 'HELLO': 'Hello there!' };
const i18n = new I18N({ phrases });

// ...


// ... routes go here ...



i18n.translate(key, locale, ...args)

Returns translation for phrase key with the given locale. Optionally pass additional arguments, e.g. format specifier replacements for use in the phrase. For example if you have a phrase of "An error occurred %s" with a key of "ERROR_OCCURRED", and you use it as such i18n.translate('ERROR_OCCURRED', 'en', 'some error message') then it would return 'An error occurred some error message.

i18n.translateError(key, locale, ...args)

Returns the same string as i18n.translate, but wrapped with a new Error object with a property no_translate set to true.

This is an extremely useful method if you are using koa-better-error-handler package in the Lad framework – as it will prevent a double translation from occurring.

i18n.middleware(ctx, next)

This middleware uses custom locale detection (in order of priority):

  1. Check URL (e.g. if /de or /de/ then it's a de locale - as long as de is a supported locale)
  2. Use the custom function (if provided by the detectLocale parameter) for locale detection
  3. Check the "locale" cookie value (or whatever the cookie option is defined as)
  4. Check Accept-Language header

It also exposes the following:

  • ctx.pathWithoutLocale - the ctx.path without the locale in it (this is used by koa-meta)
  • ctx.request - with all of i18n API methods (e.g. ctx.request.t, ctx.request.tn, ...)
  • ctx.locale - set to the value of ctx.request.locale (the current user's locale)
  • ctx.state - with all of i18n API methods (e.g. ctx.request.t, ctx.request.tn, ...)
  • ctx.state.l - a shorthand method that accepts a path and returns a localized path (e.g. ctx.state.l('/contact') will output /en/contact if the locale is "en")
  • ctx.state.availableLanguages (Array) - which is useful for adding a dropdown to select from an available language
  • ctx.state.currentLanguage (String) - the current locale's language in native language using country-language's getLanguage method
  • ctx.translate (Function) - a helper function for calling i18n.api.t or i18n.t to translate a given phrase by its property key name from the phrases object option (same as i18n.translate except it throws a ctx.throw error using Boom)
  • ctx.translateError (Function) - same as ctx.translate except it returns an Error object with a property no_translate set to true (similar to i18n.translateError)

If the given locale was not available then it will redirect the user to the detected (or default/fallback) locale.

i18n.redirect(ctx, next)

Inspired by node's language support.

Redirects user with permanent 302 redirect to their detected locale if a valid language was not found for them.

NOTE: As of v1.2.2 we have added a ignoredRedirectGlobs option you can pass to new I18N({ ... }) which will ignore these paths for locale redirection. This is incredibly useful if you are using authentication providers and the passport library, e.g. you want to set /auth/github/ok as the callback URL for GitHub, but a redirect to /en/auth/github/ok would have occurred, thus causing authentication to fail due to a bad code. In this case, you would set { ignoredRedirectGlobs: [ '/auth/**/*' ] } or simply [ '/auth/google/ok' ]. This package uses multimatch internally which supports an Array, therefore you could negate certain paths if needed. See the documentation for multimatch for more insight.

It also sets the cookie locale for future requests to their detected locale.

This also stores the last_locale (or whatever you configure the property name to be in the config option lastLocaleField) for a user via ctx.state.user.save().

NOTE: As of v3.0.0 we have added a redirectIgnoresNonGetMethods (Boolean) option (defaults to true) which you can pass to new I18N({ ... }) which will ignore non-GET methods on redirection.


We use i18n options per https://github.com/mashpie/i18n-node#list-of-all-configuration-options

Default options are as follows and can be overridden:

const i18n = new I18N({
  phrases: {},
  logger: console,
  directory: resolve('locales'),
  locales: ['en', 'es', 'zh'],
  cookie: 'locale',
  cookieOptions: {
    // Disable signed cookies in NODE_ENV=test
    signed: process.env.NODE_ENV !== 'test'
  expiryMs: 31556952000, // one year in ms
  indent: '  ',
  defaultLocale: 'en',
  // `process.env.I18N_SYNC_FILES`
  syncFiles: true,
  // `process.env.I18N_AUTO_RELOAD`
  autoReload: false,
  // `process.env.I18N_UPDATE_FILES`
  updateFiles: true,
  api: {
    __: 't',
    __n: 'tn',
    __l: 'tl',
    __h: 'th',
    __mf: 'tmf'
  register: i18n.api,
  lastLocaleField: 'last_locale',
  ignoredRedirectGlobs: [],
  redirectIgnoresNonGetMethods: true,
  // <https://github.com/ljharb/qs>
  stringify: {
    addQueryPrefix: true,
    format: 'RFC1738',
    arrayFormat: 'indices'
  redirectTLDS: true,
  // function that allows using a custom logic for locale detection (can return promise)
  detectLocale: null

If you wish to bind logDebugFn, logWarnFn, and logErrorFn per i18n options:

const i18n = new I18N({
  logDebugFn: console.log,
  logWarnFn: console.log,
  logErrorFn: console.log

We recommend to use CabinJS for all your logging needs.

For a list of all available locales see i18n-locales.

Redirect exceptions

If the path has an extension, then it is not redirected.

However if redirectTLDS option is true (which is true by default as of v4.0.0), then if the path basename ends with a valid TLD, then it is redirected.

We came across this missing feature and added it after our discovery through Forward Email.


Name Website
Nick Baugh http://niftylettuce.com/
shadowgate15 https://github.com/shadowgate15


MIT © Nick Baugh