And of course England has its own flag, which is not the same as that of Great Britain. And of course quite a few countries still using English because they were formerly colonized/oppressed/etc. (take your pick) and might have a thing or two to say about having to deal with the British flag.
There are a lot more languages than countries. And language variations, dialects, etc. And a lot of flag / language combinations are confusing, insulting, historically incorrect, or not that helpful. Like the British, the French were all over the place and there are lots of places that speak French that don't use the French flag. Likewise Spanish is used all over the Americas. India has about 21 official languages (I think, might be more). One of which is English. So, it's complicated for English and it doesn't really get any better for other languages.
Telling people to grow a tougher skin isn't particularly user friendly or that helpful.