"Sugar's used in sweets."
Translation:Η ζάχαρη χρησιμοποιείται στα γλυκά.
Hello Jaye. The question is what belongs in a course of the type you're designing. "Sugar is" is the correct English. Sugar's can be used informally, but it's slang. I'm a simultaneous interpreter and an instructor of interpreters in the national defence school. In teaching any foreign language, we first teach only the correct form. Slang comes only after true fluency is achieved and tested. Oh, and I'm a millennial. Thanks for all you do for DL. Hope this helps.
I think it is acceptable in spoken language and in literature if writing dialogue but not in formal writing. Then again Im a kid from Brooklyn so what do I know :-)
Cambridge dictionary site: