From my understanding the “Japanese IME is not ready yet.” (or Chinese) error started appearing sometime around 1903 was released. There are tons of articles and questions on internet regarding this issue with not many working solutions. Especially for restricted corporate environment. We have started seeing reports about this error while pushing 20H2 version. But it seems such problems were also observed after 1903 update (or maybe even earlier) and some IT staff was “fixing” it by copying IME files from older version into new essentially replacing it. This doesn’t work with latest Windows 10 versions. Not to say this is not a pretty solution anyway. I had to involve Microsoft support recently to tackle this and below are my findings and kind of a solution for this.