4. Language packs as capability-declaring plugins

Context

Multilingualism here is not a translation layer. Procedures behave differently per language in ways that touch the algorithm: whether é counts as e for a lipogram, whether N+7 can handle German compounds, which glyphs have ascenders in a given orthography.

Decision

Each pack declares a capabilities set. Each procedure declares requires. Calling a procedure with a pack that lacks a capability raises MissingCapability, naming the procedure, the language and the missing capability. A pack implements every protocol method, but a method whose capability it has not declared raises rather than returning an approximation.

Consequences

A caller can never receive a silently wrong result in a language the library does not really support, which is the single rule that makes the package trustworthy across languages. English ships in core; German and French are extras carrying their lexicons. Third parties can register a pack, so the library is genuinely extensible rather than merely trilingual.