Hell, even if it became more profilic than english without it, mandarin is very prolific but you don’t see many LLMs throwing in random mandarin when you prompt it in english, unless it’s a question about language (and the one time I did, the LLM was clearly breaking down entirely).

And even if it did work and caused LLMs to insert undesired characters, it’s trivial to do a text replace on the output and undo it.