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koa locales, i18n solution for koa
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LICENSE fix: make sure signed=false on set/get cookie (#24) Jan 13, 2017


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koa locales, i18n solution for koa:

  1. All locales resources location on options.dirs.
  2. resources file supports: *.js, *.json and *.properties, see examples.
  3. One api: __(key[, value, ...]).
  4. Auto detect request locale from query, cookie and header: Accept-Language.


$ npm install koa-locales --save

Quick start

const koa = require('koa');
const locales = require('koa-locales');

const app = koa();
const options = {
  dirs: [__dirname + '/locales', __dirname + '/foo/locales'],
locales(app, options);

API Reference

locales(app, options)

Patch locales functions to koa app.

  • {Application} app: koa app instance.
  • {Object} options: optional params.
    • {String} functionName: locale function name patch on koa context. Optional, default is __.
    • {String} dirs: locales resources store directories. Optional, default is ['$PWD/locales'].
    • {String} defaultLocale: default locale. Optional, default is en-US.
    • {String} queryField: locale field name on query. Optional, default is locale.
    • {String} cookieField: locale field name on cookie. Optional, default is locale.
    • {String} cookieDomain: domain on cookie. Optional, default is ''.
    • {Object} localeAlias: locale value map. Optional, default is {}.
    • {String|Number} cookieMaxAge: set locale cookie value max age. Optional, default is 1y, expired after one year.
  app: app,
  dirs: [__dirname + '/app/locales'],
  defaultLocale: 'zh-CN',


The key options.localeAlias allows to not repeat dictionary files, as you can configure to use the same file for es_ES for es, or en_UK for en.

  localeAlias: {
    es: es_ES,
    en: en_UK,

context.__(key[, value1[, value2, ...]])

Get current request locale text.

async function home(ctx) {
  ctx.body = {
    message: ctx.__('Hello, %s', 'fengmk2'),


__('Hello, %s. %s', 'fengmk2', 'koa rock!')
'Hello fengmk2. koa rock!'

__('{0} {0} {1} {1} {1}', ['foo', 'bar'])
'foo foo bar bar bar'

__('{a} {a} {b} {b} {b}', {a: 'foo', b: 'bar'})
'foo foo bar bar bar'


Get locale from query / cookie and header.


Set locale and cookie.


Where does locale come from, could be query, cookie, header and default.

app.__(locale, key[, value1[, value2, ...]])

Get the given locale text on application level.

console.log(app.__('zh', 'Hello'));
// stdout '你好' for Chinese

Usage on template

this.state.__ = this.__.bind(this);

Nunjucks example:

{{ __('Hello, %s', }}

Pug example:

p= __('Hello, %s',

Koa-pug integration:

You can set the property locals on the KoaPug instance, where the default locals are stored.

app.use(async (ctx, next) => {
  koaPug.locals.__ = ctx.__.bind(ctx);
  await next();


If you are interested on knowing what locale was chosen and why you can enable the debug messages from debug.

There is two level of verbosity:

$ DEBUG=koa-locales node .

With this line it only will show one line per request, with the chosen language and the origin where the locale come from (queryString, header or cookie).

$ DEBUG=koa-locales:silly node .

Use this level if something doesn't work as you expect. This is going to debug everything, including each translated line of text.



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