re: For those who know foreign languages, what are some weird things about English?

I'm not fluent in any other language, but my gf's first language is Mandarin. Off the top of my head some idiomatic expressions that she mixes up because they're expressed differently and she directly translates:

Instead of saying to throw something away she says to "drop it."
Instead of saying to turn off something (e.g. television, lights, air conditioning) she says to "close" it.

Pronouncing vowels are a point that she struggles with. For English speakers a hard part of learning Mandarin are learning the tones, but similarly native mandarin speakers can have a hard time with English vowel pronunciations. There are distinctions in vowels for english that don't exist in mandarin, so some vowels that sound very different to a native English speaker will sound the same to a native Mandarin speaker.