I'm trying. But it's hard to write not in the way I pronounce. And it's not always possible to spot it in my own writing.
Maybe there's a list of words/phrases that a non-native shouldn't use>
You can write common contractions like
don't, won't, I'm, he'd, etc.
Gonna and
wanna are phonetic spellings of common pronunciations of
going to and
want to. These spellings have never been adopted in formal writing except in dialog.
Wanna seemed to pop up all over the place in the last few years, and I notice it particularly frequently in online writings by non-native speakers. It looks to me like a sign of trying too hard to fit in, though I'm sure it just flows naturally off the fingers of those who use it.
Regardless of how older American readers may react to seeing them, the real reason not to use
wanna and
gonna on this forum is that we promote the kind of English you can use in job applications, academic papers, business memos, etc. Those words are in an informal register that's unsuitable in those contexts.