mew-ton If you are using Starlight's i18n features to publish your documentation in multiple languages (e.g., English and Japanese), you should only set skill: true on the English pages.
Why Default to English?
System prompts and base tools for most modern LLMs (including Claude) are primarily tuned in English. Providing the skill's instructions, frontmatter descriptions, and rules in English yields the highest accuracy and reduces localized misinterpretation.
Therefore, do not set skill: true on your translated pages (e.g., ja/best-practices/01-one-instruction-per-file.md).
Instead, maintain the English document as the sole machine-readable skill, while keeping the translated pages as human-readable documents only. This ensures that regardless of the user's localized browser language, the AI agent always references the optimal English instructions.