In Tokyo it is possible to get a job as a software developer without speaking Japanese. After living here a couple years someone decides they like life here, but want to run their own business. Maybe they want to run a SaaS or something that targets a global audience. For visa purposes, they need a Japanese company.
By this time they’ve maybe picked up up some basic Japanese but aren’t fluent. Becoming fluent in a language is quite challenging, especially if you’re working full time in an English language environment. Even without fluency, it’s possible to enjoy life here.