Pluralization

Pluralizable locales

A pluralization in the locale files may look like the one below:

en:
  example:
    pluralization:
      one: "One item"
      other: "%{count} items"

The parser will interpret a translation as a pluralizable one if it contains a key called other, and its value contains a %{count} interpolation key.

Info

The zero category tag is a special case because it is optional in almost all pluralization rules. If it is present in the locale files and count is 0, the value for zero will be used. If not, then Rosetta will fall back to other.

Category tags

All the short category tags defined by the CLDR are supported:

• zero
• one (singular)
• two (dual)
• few (paucal)
• many (also used for fractions if they have a separate class)
• other (required—general plural form—also used if the language only has a single form)

Pluralizable translations

For pluralizable translations, the t method will require the count argument, which can be a Float or an Int:

Rosetta.find("example.pluralization").t(count: 1.0)
# => "One item"
Rosetta.find("example.pluralization").t(count: 12)
# => "12 items"

Pluralization rules

Rosetta includes pluralization rules for most of the available locales. They can be found in the repo under src/rosetta/pluralization/rule.

Custom pluralization rules

Custom rules need to inherit from Rosetta::Pluralization::Rule, define the apply method and define the required CategoryTags annotation. For example:

@[Rosetta::Pluralization::CategoryTags(:one, :few, :other)]
struct MyRule < Rosetta::Pluralization::Rule
  def apply(count : Float | Int) : Symbol
    case count
    when 1
      :one
    when 2..5
      :few
    else
      :other
    end
  end
end

Info

The CategoryTags annotation is used by the parser to check if the required category tags are all present in the pluralizable translations. If the annotation is not defined, the compiler will let you know. Since zero is optional, only include it in the list if it should be required everywhere.

In the initializer Rosetta created at setup, register the rule for one or more locales:

@[Rosetta::PluralizationRules({
  en: MyRule,
  nl: MyRule,
})]
module Rosetta; end

Warning

Configuring custom rules should happen before calling the Rosetta::Backend.load macro.