What we do know is that YouKris posted the photo in early August 2024, and according to Chinese media, many of the comments are local colloquialisms that don't translate well.
Obviously, for this type of letter, you want to adhere to the instructions and the tone, so feel free also to use phrasal verbs and colloquialisms, any slang.
Idiomatic language does not mean idioms, idioms are a type of idiomatic language, phrasal verbs are a type of idiomatic language, slang, colloquialisms, local language that you'll hear around here, that's another.