How does internationalization work in JavaScript?

I'm wondering how to deal internationalization in JavaScript. I googled but I'm not getting convincing answers for:

• Does JavaScript have native support for internationalization?
• What is i18n in JavaScript?
• How to deal with calendars, currencies, dates, etc.?

I've already read https://stackoverflow.com/questions/934175/internationalization-inside-javascript.

Localization support in legacy browsers is poor. Originally, this was due to phrases in the ECMAScript language spec that look like this:

>Number.prototype.toLocaleString()
>Produces a string value that represents the value of the Number formatted according to the conventions of the host environment’s current locale. This function is implementation-dependent, and it is permissible, but not encouraged, for it to return the same thing as toString.

Every localization method defined in the spec is defined as "implementation-dependent", which results in a lot of inconsistencies. In this instance, Chrome Opera and Safari would return the same thing as .toString(). Firefox and IE will return locale formatted strings, and IE even includes a thousand separator (perfect for currency strings). Chrome was recently updated to return a thousands-separated string, though with no fixed decimal.

For modern environments, the ECMAScript Internationalization API spec, a new standard that complements the ECMAScript Language spec, provides much better support for string comparison, number formatting, and the date and time formatting; it also fixes the corresponding functions in the Language Spec. An introduction can be found here. Implementations are available in:

• Chrome 24
• Firefox 29
• Internet Explorer 11
• Opera 15

There is also a compatibility implementation, Intl.js, which will provide the API in environments where it doesn't already exist.

Determining the user's preferred language remains a problem since there's no specification for obtaining the current language. Each browser implements a method to obtain a language string, but this could be based on the user's operating system language or just the language of the browser:

// navigator.userLanguage for IE, navigator.language for others
var lang = navigator.language || navigator.userLanguage;

A good workaround for this is to dump the Accept-Language header from the server to the client. If formatted as a JavaScript, it can be passed to the Internationalization API constructors, which will automatically pick the best (or first-supported) locale.

In short, you have to put in a lot of the work yourself, or use a framework/library, because you cannot rely on the browser to do it for you.

Various libraries and plugins for localization:

• Mantained by an open community (no order):

• Polyglot.js - AirBnb's internationalization library
• Intl.js - a compatibility implementation of the Internationalisation API
• i18next (home) for i18n (incl. jquery plugin, translation ui,...)
• moment.js (home) for dates
• numbro.js (home) (was numeral.js (home)) for numbers and currency
• l10n.js (home)
• L10ns (home) tool for i18n workflow and complex string formatting
• jQuery Localisation (plugin) (home)
• YUI Internationalization support
• jquery.i18Now for dates
• browser-i18n with support to pluralization
• counterpart is inspired by Ruby's famous I18n gem
• jQuery Globalize jQuery's own i18n library
• js-lingui - MessageFormat implementation for JS (ES2016) and React

• Others:

• jQuery Globalization (plugin)
• requirejs-i18n Define an I18N Bundle with RequireJS.

Feel free to add/edit.

Mozilla recently released the awesome L20n or localization 2.0. In their own words L20n is

> an open source, localization-specific scripting language used to process gender, plurals, conjugations, and most of the other quirky elements of natural language.

Their js implementation is on the github L20n repository.

Some of it is native, the rest is available through libraries.

For example Datejs is a good international date library.

For the rest, it's just about language translation, and JavaScript is natively Unicode compatible (as well as all major browsers).

You can also try another library - https://github.com/wikimedia/jquery.i18n .

In addition to parameter replacement and multiple plural forms, it has support for gender a rather unique feature of custom grammar rules that some languages need.