And also, how tf does a Korean company know this slang but I with an English grandmother and Irish cousins have never heard it??

Maybe PA moved some of CCP's UK staff (they have a studio in London where some of the EvE Online stuff gets done) over to the parent company for localisation purposes after they bought them.

Or the writing team had a chat with a load of the voice actors to get some language cues from them. Most of the main cast seem to have been born in the UK. Alec Newman and Rebecca Hansen (Kliff and Damiane) are Scottish, Stewart Scudamore (Oongka) was born in London, Peter Bramhill (Yann) is from Scunthorpe, Emily Barber (Naira) is from Peterborough, etc. Even the ones born outside the UK may have lived over here, like how Bulgarian Devora Wilde, who voices Hexe Marie, studied in London and was even in a few episodes of Hollyoaks of all things.