Plural Rules in ICU MessageFormat

Understanding ICU Plural Rules

Pluralization is one of the most powerful features of ICU MessageFormat. Unlike naive approaches that only handle singular vs. plural, ICU uses the Unicode CLDR plural rules which define up to six categories depending on the language.

The Six Plural Categories

Category	Used By	Example Numbers (English)
zero	Arabic, Latvian	N/A in English
one	English, German, Spanish	1
two	Arabic, Hebrew, Slovenian	N/A in English
few	Polish, Czech, Russian	N/A in English
many	Polish, Arabic, Russian	N/A in English
other	All languages (required)	0, 2, 3, 4, 5, ...

English Plural (2 categories)

English only uses one (for exactly 1) and other (for everything else):

{count, plural,
    one {You have # new notification}
    other {You have # new notifications}
}

Polish Plural (4 categories)

Polish uses one, few, many, and other:

{count, plural,
    one {# plik}
    few {# pliki}
    many {# plików}
    other {# pliku}
}

• 1 plik (one)
• 2, 3, 4 pliki (few)
• 5-21 plików (many)
• 1.5 pliku (other)

Arabic Plural (6 categories)

Arabic uses all six categories:

{count, plural,
    zero {لا كتب}
    one {كتاب واحد}
    two {كتابان}
    few {# كتب}
    many {# كتاباً}
    other {# كتاب}
}

Exact Value Matching with =N

You can match exact numeric values using =N syntax, which takes priority over category matching:

{count, plural,
    =0 {Your inbox is empty}
    =1 {You have one message}
    =42 {You have the answer to everything}
    other {You have # messages}
}

The # Placeholder

Inside plural cases, # is replaced with the formatted numeric value:

{count, plural, one {# item} other {# items}}
count=1    -> "1 item"
count=42   -> "42 items"
count=1000 -> "1,000 items" (with locale formatting)

Always Include other

The other category is required in every plural message. It acts as the default fallback when no other category matches. Omitting it will cause runtime errors in most ICU implementations.