Google does not know multilingual people exist

This has to do with the authors specific workflow as a professional translator. As a person who has a number of niche workflows this is just something you get used to. If you have niche needs then sometimes you need a niche product or something custom to workaround the problem. I don't think this has anything to do with people who are multilingual -- I only have anecdata so I'll phrase it as a conjecture: almost everyone, even people who are multilingual, probably search in a single language.