... might sound like a reasonable solution until you start trying to write about languages. It is unreasonable for a sentence like "In Japanese, the word for 'hello' is こんにちは; in Korean, it's 안녕하세요." to be unrepresentable.
Then language change tags which draw a box around the different language.
Why use that when a "simple" dictionary structure mapping codepoint to language exists? It's called Unicode.
We tried that in the 1980s with MS/PC/DR-DOS and code pages. We also had BBS networks where people shared such files around the world. One language per file turned out to be a bad idea.
To be fair, that was actually one language per computer.
Oh, it really wasn't. If you want the terrible reality, start with how FidoNet CHARSET and CHRS 'kludge lines' tried to make this work.