Localization in Elm with Plurals Support

April 05, 2018 in elm, functional programming

Here’s the example of how you can localize your Elm application including plurals support.

The code is available in elm-samples repository. It is based on the Elm i18n and Type Safety article by Amitai Burstein. Their solution provides the localization functionality with type safety.

The difference of my code is that I’ve added support for plurals.

Live demo:

Plurals Support

The logic for a pluralization is implemented in the PluralRules.elm file.

The PluralRules module exports functions that can be used for pluralized translation for a particular language.

As an example, there are functions for english, french, russian, and german languages.

Plural rules for a language can be found at the Unicode site. Different languages vary in how they support plurals, thus the amount of translations for a particular language will vary. This means that every translation function will take different amount of parameters.

For example, english function takes two translations (one and other), and a number of items to provide the right plural form:

english : String -> String -> Int -> String
english "Apple" "Apples" 10 -- will evaluate to "Apples"

The russian function requires four translations (one, few, many, and other):

russian : String -> String -> String -> String -> Int -> String
-- example:
russian "Яблоко" "Яблока" "Яблок" "Яблока" 10 -- will evaluate to "Яблок"

How to Add Pluralization for New Language

Let’s add a support for a German language. Here’s the rules table from the Unicode site: german plural rules

German language requires two translations for cardinal numbers: one, and other. The Rules column contains the rules for pluralization, where:

  • i is the integer digits of n.
  • v is the number of visible fraction digits in n, with trailing zeros.

The implementation for this logic in Elm:

german : String -> String -> Int -> String
german one other number =
    let
        v =
            visibleFractionDigits number

        i =
            integerDigits number
    in
    if v == 0 && i == 1 then
        one
    else
        other

Support for other languages can be added in a similar manner:

  1. Find the plural rules for a language in the Unicode table.
  2. Implement the rules in Elm as a separate function.
  3. Use the function in your code.
April 05, 2018 in elm, functional programming
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