@fluent/langneg

@fluent/langneg

@fluent/langneg is an API for negotiating languages. It's part of Project Fluent, a localization framework designed to unleash the expressive power of the natural language.

It's main function is to provide functionality around the Intl.Locale API with a focus on language negotiation, matching and selection.

Installation

@fluent/langneg can be used both on the client-side and the server-side. You can install it from the npm registry or use it as a standalone script.

npm install @fluent/langneg

How to use

import { negotiateLanguages } from '@fluent/langneg';

const supportedLocales = negotiateLanguages(
  navigator.languages,       // requested locales
  ['de', 'en-US', 'pl'],     // available locales
  { defaultLocale: 'en-US' }
);

The API reference is available at https://projectfluent.org/fluent.js/langneg.

Strategies

The API supports three negotiation strategies:

filtering (default)

In this strategy the algorithm will look for the best matching available locale for each requested locale.

Example:

requested: ['de-DE', 'fr-FR'] available: ['it', 'de', 'en-US', 'fr-CA', 'de-DE', 'fr', 'de-AU']

supported: ['de-DE', 'fr']

matching

In this strategy the algorithm will try to match as many available locales as possible for each of the requested locale.

Example:

requested: ['de-DE', 'fr-FR'] available: ['it', 'de', 'en-US', 'fr-CA', 'de-DE', 'fr', 'de-AU']

supported: ['de-DE', 'de', 'fr', 'fr-CA']

lookup

In this strategy the algorithm will try to find the single best locale for the requested locale list among the available locales.

Example:

requested: ['de-DE', 'fr-FR'] available: ['it', 'de', 'en-US', 'fr-CA', 'de-DE', 'fr', 'de-AU']

supported: ['de-DE']

API use:

let supported = negotiateLanguages(requested, available, {
  strategy: 'matching',
});

Likely subtags

Fluent Language Negotiation module carries its own minimal list of likely subtags data, which is useful in finding most likely available locales in case the requested locale is too generic.

An example of that scenario is when the user requests en locale, and the application supports en-GB and en-US.

Learn more

Find out more about Project Fluent at projectfluent.org, including documentation of the Fluent file format (FTL), links to other packages and implementations, and information about how to get involved.