Basic i18n translation.
Last updated 3 years ago by leichtgewicht .
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$ cnpm install i18n-core 
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i18n-core is a no-fuzz Node.js implementation of i18n. It doesn't connect to express or any other fancy Node framework and is extensible where it needs to be and allows to reduce the complexity of other i18n implementations (thus the name).

It implements basic variable replacements in the mustache and sprintf manner.


To use i18n-core all you need to do is install it using npm

npm i i18n-core --save


var i18n_core = require('i18n-core')
var i18n = i18n_core({greeting: 'hello!'})
i18n.__('greeting') // hello!

To have different namespaces for different languages you can get a prefixed translations using .section().

var i18n = i18n_core({
  en: { greeting: 'hello!' },
  de: { greeting: 'guten tag!' }

var en = i18n.section('en')
en.__('greeting') // hello!

var de = i18n.section('de')
de.__('greeting') // guten tag!

Note: .section(<section>) is the same thing as .prefix(<section> + '.')


The system is based on lookup implementations that allow the system to use different sources to get its strings from. The examples before used an object and because of this the former example would be equal to:

var i18n = i18n_core(require('i18n-core/lookup/object')({greeting: 'hello!'}))

If you were to pass in a string to i18n-core instead like this:

var i18n = i18n_core('./')

Then it would be equal the primitive file-system lookup same like this:

var i18n = i18n_core(require('i18n-core/lookup/fs')('./'))

You can pass in your own strategy by given an object to the constructor that contains a "get"-method:

var i18n = i18n_core({
  get: function (key) {
    return null // Who needs translation anyway?

In case you need to have several strategies that need to be chained you can use the chain lookup:

var i18nChain = require('i18n-core/lookup/chain')
var i18nObject = require('i18n-core/lookup/object')
var i18n = i18n_core(i18nChain(i18nObject({a: 'x'}), i18nObject({a: 0, b: 1})))
i18n.__('a') // x
i18n.__('b') // 1

In case you have an i18n object that you want to use as lookup for another i18 object you can extend them:

var i18nExtend = require('i18n-core/lookup/extend')
var i18nObject = require('i18n-core/lookup/object')
var i18nA = i18n({a: 'x'})
var i18nB = i18n(i18nExtend(i18nA, i18nObject({
  b: 1

i18n.__('a') // x
i18n.__('b') // 1


i18n-core does implement basic placeholder replacements like:

en.__('%s is cool', 'he') // 'he is cool'

following the logic of sprintf.

It also offers mustache-like pattern replacement like this:

en.__('{{name}} are cool too', {name: 'you'}) // 'you are cool too'

Substitution variants

By default i18n-core does not have any dependencies and the default substitution is mustache-like and sprintf-like with limited compatibility.

Note: Without mustache and sprintf installed, it will use require('i18n-core/simple')

In order to get full compatibility you can simply install the peer dependency.

npm i mustache sprintf --save

Note: With mustache and sprintf installed, it will use require('i18n-core/full')

It is furthermore possible to customize the formatting by specifying own implementations:

var i18n_core = require('i18n-core')
i18n_core.mustache = require('mustache')
i18n_core.vsprintf = require('sprintf').vsprintf

Advanced Namespaces

It is possible to chain translation prefixes like this:

var at = i18n_core({de:{at: {hello: 'Zewas!'}}}).section('de').section('at')
at.__('hello') // Zewas!

and you can also change the chain if you want to.

var translate = i18n_core({
  de: {title: 'Meine Webseite'},
  en: {title: 'My Website'}
}).section('de', true) // <- this true is important :)
translate.__('title') // Meine Website
translate.__('title') // My Website

To prevent malicious use the changing of the section is prevented unless you pass a true flag to it.

In some instances it is necessary to know in advance if a key has a value or not, in this case you can use has.

var translate = i18n_core({title: 'My Website'})
translate.has('title') // true
translate.has('subtitle') // false

Additionally, for module development, its possible to access the raw data using raw:

var translate = i18n_core({no: {val: 5}})
translate.raw('no') // {val: 5}

Listening to changes

Since you can change translation nodes it is, in an interactive environment, good to have a way to be informed about changes. i18n-core has a very light-weight and fast event implementation tailored to the process.

const parent = i18n_core({
  de: {
    site: {
      title: 'Meine Webseite'
  en: {
    site: {
      title: 'My Website'
}).section('de', true)
const translate = parent.section('site')
translate.__('title') // Meine Webseite
translate.on('contextChange', function () {
  translate.__('title') // My Website

Absolute Lookups

i18n-core supports the use of absolute roots. Absolute roots allow to lookup entries in absolute locked roots rather than the given level.

var translate = i18n_core({
  title: 'Meine Webseite',
  sectionA: {
    title: 'Lebenslauf'

var sub = translate.section('sectionA')
sub('title') // Lebenslauf
sub.abs('title') // Meine Webseite

This allows to crate things like footers where you can pass one section to a module and it is still able to access absolute code.

However, this also creates the problem that subsections (for languages) can be escaped from. In order to prevent that, you can lock the absolute root to .lock(). You can lock any section and any subsequent sections will get the same root.

var translate = i18n_core({
  de: {
    title: 'Meine Webseite',
    sectionA: { title: 'Lebenslauf' }
  en: {
    title: 'My Website',
    sectionA: { title: 'Curriculum Vitae' }
var lang = translate
  .section('de', true)
  .lock() // This locks the absolute root to the language level

var sub = lang.section('sectionA')
sub('title') // Lebenslauf
sub.abs('title') // Meine Webseite

sub('title') // Curriculum Vitae
sub.abs('title') // My Website

Prefixing every absolute lookup with abs can get tedious that is why there is also the possibility to use absSection that, like section, returns a new translation object where every call assumes a particular absolute section.

var translate = i18n_core({
  en: {
    sectionA: {
      title: 'Curriculum Vitae'
    menu: {
      about: 'About Me'
var lang = translate.section('en', true).lock()

var sectionA = lang.section('sectionA')
sectionA('title') // Curriculum Vitae
var menu = sectionA.absSection('menu')
menu('about') // About Me

For your convenience there is also the .root() alias for .absSection('').

Core API's

The default API is made to provide a simple solutions to common problems but i18n-core also offers a reduced, faster API without conveniences. You can get access to the core by using require('i18n-core/core').

var core = require('i18n-core/core')({
  get: function lookupValue (key) {
    return // Return a value for the key or undefined
}, function translate (value, fallbackKey, namedArgs, args) {
  // value ......... value that should be translated
  // fallbackKey ... fallbackKey that should be passed on to `fallback`
  // namedArgs ..... named arguments passed in through the API, can be undefined
  // args .......... regular arguments passed in through the API, can be undefined
core.get(key) // looks up a key
core.has(key) // .get(key) !== undefined

// translate the key with named & regular args
core.translate(key, namedArgs, args)

// translate the first found entry with a fallback
// keys .......... Array of keys to test
// fallbackKey ... Key to be passed on to `fallback`
// namedArgs ..... `namedArgs` to be used when translating
// args .......... `args` to be used when translating
core.translateFirst(keys, fallbackKey, namedArgs, args)

// Creates an api node where each key is prefixed
// prefix .............. prefix to be set for each translation request
// allowModification ... allows changePrefix API
core.prefix(prefix, allowModification)

// Creates an api node where each key is prefixed to an absolute root
// prefix .............. prefix to be set for each translation request
// allowModification ... allows changePrefix API
core.absPrefix(prefix, allowModification)

// Changes the prefix of the API (undefined when modification forbidden)
core.lock(locked) // Locks, unlocks the absolute root.
core.absRoot // Holds the root fallback

// Fields used for internal processing
core.parent // Parent node (or undefined)
core.translator // Quick lookup of the translation method
core.currentPrefix // Prefix of the current node '' == null

core.on(type, handler) // Listen to changes of `changeContext`
core.off(type, handler) // Remove the handler


If you have any questions, please post them as issue, thanks!

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