Languages have different numbers of plural forms

What it is

Locale-specific plural categories are sets of grammatical responses triggered by quantity that differ among languages. Unicode CLDR exposes zero, one, two, few, many, and other. These are not literal English meanings; they label categories demonstrated by grammatically forced changes in minimal pairs. A locale uses only a subset, with other as the required fallback.

Why it happens

Grammatical number may surface on nouns, verbs, pronouns, adjectives, or case marking. CLDR computes operands from source number N and its representation: v counts visible fraction digits including trailing zeros, w excludes trailing zeros, f treats the visible fraction including trailing zeros as an integer, and t excludes them. Thus 1, 1.0, and 1.00, or 1.3 and 1.30, can differ under rules that use these operands. Integer and modular conditions also occur; cardinal and ordinal rules use separate data and templates. An API that first erases visible precision cannot reconstruct these operands later.

Studying it

Validation has three layers. First, compare the runtime's category output for official samples and integer/decimal boundaries with the current CLDR rules, passing values through the product formatter so trailing-zero information is preserved. Second, use a set of minimal-pair templates: only the number changes, and wording changes only where grammar forces them; multiple nouns or constructions may be needed to expose every category. Native-language experts judge agreement and acceptability. Only for critical UI risk should a third layer add a real comprehension task and measure choice errors. Cardinal and ordinal validation require separate templates.

Where it stops holding

CLDR categories are a message-selection interface, not a complete linguistic account of grammatical number. Case, gender, and lexical choice can still vary within one category. Rules can be revised as evidence changes, so use the CLDR data shipped by the runtime. Exact =0 matches numeric zero, while a locale may lack a zero category and classify zero as one or other; likewise one need not contain only integer one. Product exceptions and language categories are separate mechanisms.

Applying it

• Use a mature localized message formatter backed by CLDR instead of coding count == 1 in business logic.
• Configure cardinal and ordinal selection separately, supply categories the locale produces, and retain other; express product exceptions with the formatter's explicit exact-value selector rather than disguising them as zero or one.
• Give translators complete messages so each branch can adjust nouns, verbs, pronouns, and word order rather than swapping a suffix.
• Generate representative and decimal-boundary cases from the runtime's current rules, render every branch, and obtain native-language grammatical review.

Related

• Same group: S1.04.2 Noun gender affects articles and adjectives · S1.04.3 Singular/plural pairs cannot cover most languages · S1.04.4 Zero quantities need a distinct expression
• Adjacent: S1.05 Translation context and string reuse · S1.06 Word-order problems in concatenated strings
• Search terms: CLDR plural rules · minimal pairs · grammatical number