The last time I worked on a localized project, we had a technical fake language present in non-release envs. It was generated with every build (it was just a simple .po file, so easy to handle), and it was the same as English, but had an "x" at the start and end of each text, so you knew that it was "translated" (or at least it was translatable, and not hardcoded). QA included checking this fake language - if they found any text without X's around it, it was a clear sign of a i18n bug.
That's cool! We used machine translate to hindi for this which made it super obvious what was english / not as it was different character set (but made it hard to navigate)
Looking for something to help with DX though here, not QA
https://platform.claude.com/docs/en/about-claude/pricing puts input token pricing at $3/M tokens. Assuming this was ALL input, that's over $2400 in API for $40/month