[translator] Epic: translation style controls — glossary, tone & brand voice

[SearheiParkhamchuk]

Summary

Add first-class, structured control over how content is translated — a glossary, tone/voice, and protected (do-not-translate) terms — instead of relying only on a free-form system prompt.

Motivation

Comparable tools (e.g. Sanity AI Translations) expose brand-voice controls as structured, maintainable settings rather than prompt text:

• a glossary of preferred/forbidden term translations per locale, with a do-not-translate flag;
• a style guide for formality and tone/voice;
• protected phrases the model must never translate (brand names, product names, set terms).

Today our plugin can only influence this through the system prompt, which is hard to maintain, not per-term, and not enforceable. This epic closes the most significant capability gap versus Sanity.

Scope (high-level — to be refined)

• Glossary: preferred and forbidden translations per term, per target locale; a do-not-translate flag.
• Tone / style: formality and voice guidance applied consistently to translation requests.
• Protected terms/phrases: a hard constraint so listed terms are passed through untranslated.
• Make these editable and maintainable (config and/or editor-facing) and feed them into the translation prompt automatically.
• Consider hard (rule-based) vs soft (prompt-level) enforcement, and how quality is validated.

Notes

• Data model, enforcement strategy and UX to be defined in follow-up sub-issues.
• Relates to the async system-prompt builder (translator: an async systemPrompt builder with collection, document and run context #109) and the provider abstraction.

Priority: High. Details are intentionally high-level for now; sub-issues will follow.