Technically speaking, the Zweihänder and the Claymore are different weapons. They're similar, though, yes. I've often seen people writing "Zweihander" in English so you could say writing it the proper way is a good hint, though.
Like with all things, practice makes perfect. I keep learning new phrases and the like in English as well. And for spelling and grammar, there are also tools like Grammarly to help you out.