er1c / scala-java-locales   0.1


Implementation of java locale for scala.js

Scala versions: 2.12
Scala.js versions: 0.6


Build Status Scala.js

scala-java-locales is a clean-room BSD-licensed implementation of the java.util.Locale API and related classes as defined on JDK8, mostly for Scala.js usage. It enables the locale API in Scala.js projects and supports usage requiring locales like number and dates formatting.


Simply add the following line to your sbt settings:

libraryDependencies += "com.github.cquiroz" %%% "scala-java-locales" % "0.3.1-cldr30"

If you have a crossProject, the setting must be used only in the JS part:

lazy val myCross = crossProject.
    libraryDependencies += "com.github.cquiroz" %%% "scala-java-locales" % "0.3.1-cldr30"

Requirement: you must use a host JDK8 to build your project, i.e., to launch sbt. scala-java-locales does not work on earlier JDKs.

Work in Progress / linking errors

This library is a work in progress and there are some unimplemented methods. If you use any of those on your Scala.js code, you will get linking errors.


The API follows the Java API for Locales, any major difference should be considered a bug. However, to avoid loading all the data for locales you need to explicitly install locales you want to use outside the set of standard locales

You can do that by, e.g. installing the Finnish locale

import locales.LocaleRegistry

// Install the locale

// Now you can use the locale
val dfs = DecimalFormatSymbols.getInstance(Locale.forLanguageTag("fi_FI"))

Note: that calls to Locale.forLanguageTag("fi_FI") will succeed regardless of the installation due to the requirements on the Locale API

Default Locale

It is highly recommended that you set a default locale for your application with, e.g.


The Java API requires a default Locale though it doesn't mandate a specific one, instead, the runtime should select it depending on the platform.

While the Java Locales use the OS default locale, on Scala.js platforms like browsers or node.js, there is no reliable way to identify the default locale. scala-java-locales sets en (English) as the default locale and does not attempt to determine the correct locale for the environment. This is a desigs decision to support the many API calls that require a default locale. It seems that Scala.js de facto uses en for number formatting.


java.util.Locale is a relatively simple class and by itself it doesn't provide too much functionality. The key for its usefulness is on providing data about the locale especially in terms of classes like java.text.DecimalFormatSymbols, java.text.DateFormatSymbols, etc. The Unicode CLDR project is a large repository of locale data that can be used to build the supporting classes, e.g. to get the DecimalFormatSymbols for a given locale.

Most of this project is in the form of code generated from the CLDR data. While many similar projects will create compact text or binary representation, this project will generate class instances for locale. While this maybe larger at first, Scala.js code optimization should be able to remove the unused code during optimization.

Starting on Java 8, CLDR is also used by the JVM, for comparisons the java flag -Djava.locale.providers=CLDR should be set.

Note: Java 8 ships with an older CLDR version, specifically version 21. scala-java-locales uses the latest available version, hence there are some differences between the results and there are new available locales in scala-java-locales.


Locales and the CLDR specifications are vast subjects. The locales in this project are as good as the data and the interpretation of the specification is. While the data and implementation has been tested as much as possible, it is possible and likely that there are errors. Please post an issue or submit a PR if you find such errors.

In general the API attempts to behave be as close as possible to what happens on the JVM, e.g. the numeric system in Java seems to default to latn unless explicitly requested on the locale name.


A very simple Scala.js project is available at scalajs-locales-demo


scala-java-locales explicitly doesn't have any dependencies. The sbt project has some dependencies for code generation, in particular treehugger but they don't carry over to the produced code


scala-java-locales uses Semantic Versioning and includes the CLDR version used as a build tag, e.g.:

0.3.1-cldr30 // Version 0.3.1 with CLDR version 30


Copyright © 2016 Carlos Quiroz

scala-java-locales is distributed under the BSD 3-Clause license.