ADR 0007: Multilingual — architect for five, ship two; the rest as locale packs

Status: accepted · Date: 2026-06-17

Immutable record. Exempt from drift tracking (no covers). Supersede, don't edit.

Part of the 0002 product direction. Gated by 0003.

Context

The goal is a worldwide user base: Chinese first, eventually Chinese / English / Japanese / Italian / German. "Multilingual" is layered — answer language, deterministic message strings (currently hardcoded Chinese), input parsing, retrieval tokenization (BM25 is CJK uni+bigram; Japanese wants real segmentation; Italian/German want stemming), and per-language evaluation. Shipping Chinese-only risks under-designing the abstraction needed for the later five-language expansion.

Decision

Architect for five, ship two. Thread a locale seam through all layers — tokenizer registry, message catalog, intent vocabulary, prompt templates — each locale-keyed and Protocol-pluggable like everything else. Ship and test Chinese + English in core. English is the second language deliberately: it is the OSS lingua franca, and being non-CJK it forces the tokenizer/stemming/space-delimited abstraction to be real rather than CJK-only. Japanese / Italian / German ship as community locale packs with a contributor checklist.

Alternatives considered (rejected)

• Output-locale only / thin i18n (option A): locale controls answer language + a message catalog; input/tokenization/corpus unchanged. Rejected — under-designs the seam for the five-language goal.
• Full per-language pipeline localization now (option B): all five languages first-class immediately. Rejected — build the seam and two reference locales, not five.

Consequences

• Locale packs are a concrete test of the Protocol extension story for outsiders, reinforcing the OSS-library identity (0003).
• Locale-keyed prompt templates are realized by 0008.
• Per-language intent vocabulary interacts with the parser decision in 0010.
• New artifacts: LocaleProfile, a tokenizer registry, a message catalog, a "how to add a locale" guide.