This has been a long time coming. I remember they started working on this back when Microsoft switched to Chromium. If I recall correctly, back then a Microsoft engineer was doing a lot of the implementation. I wonder if the DevTools team's refactoring of their codebase [1] had a lot of impact on this i18n/l10n work?
[1]: https://developer.chrome.com/blog/migrating-to-typescript/ for example