The rule
The agent answers in the language of the first message of the session. The interface language sets how slash commands expand and what the survey and chrome look like — so a session started in Korean stays Korean even if you switch the interface to English later.
Fixes
- Start a new chat after changing the interface language.
- Or say so explicitly in the next message: "From now on answer in English" — the rest of the session follows.
- For a single artifact: "rewrite the report in Japanese" revises it as a new version.
Mixed languages inside a report
References keep their original titles by design. Figure labels follow the session language; if a figure came out in English in a Korean session, ask "relabel the axes in Korean" — the figure is regenerated.
Slash command expanded in the wrong language
The expansion follows the interface language at the moment you send. Check the language menu in the footer or the profile menu, then resend.