I can't speak for the status quo, but for at least the first ~5 years (so until 3 years ago when I last attempted to use it), the JS implementation of Fluent was a mess. Constant issues with incomplete API, wrong TS typings (which at that point were external) and build/bundling issues to the point where we opted for a homebrew solution.

I imagine that I probably wasn't the only one driven away by that (and I gave it many attempts!).