Do i still have to work hard in school?

Ok before you all say yes, this is my 2nd semester in first year of high school, this will be my last one too, im going back to the UK (Wales) because i dont like schooling in the US but i mean because its my last semester will it affect me back in the UK? Like i dont speak english back in wales i speak welsh so that wont affect my grammer?

I speak six languages myself (Irish Gaelic, Welsh, Scottish Gaelic, Romanian, English and Greek)

And I often have a problem with inserting foreign grammer into my words, endiing up in what my friends call "Yoda speak" or when i get frustrated, either cursing in another tongue or translating it into English while cursing.

Does anyone else have this problem?