This chapter was actually a comment from @AzaleaDrop but I felt I had to write it as a chapter because it's important.
Too many characters are given unnecessary accents for no other reason but to make them stand out. This could be to make them seem more appealing and sexy or to make them appear more villainous. Naturally, a Mary-Sue is typically the first one.
Just make sure you have a reason why you want your character to have a particular accent and decide if it is a vital detail. If so, state why.
@AzaleaDrop also pointed out that sometimes characters use words from other languages in causal conversation. I can understand if on common words people slip up e.g. A French person saying 'merci' a lot. What is irritating is when it's very specific words like 'Baka' and 'kawaii' in Japanese get thrown in. This just makes your character seem like they are trying too hard to be foreign.
People do slip up with languages and that's normal, they're hard. But make it seem like they did accidentally make that mistake, not that they did it to purely stand out.