For example, I wish to state that it's been a long time since I used or studied Spanish, would that be?
Hace muchos años que lo usé
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Sign up to join this communityYour translation is correct however "usé" sounds like if you were talking about an object.
To better express the idea about the knowledge of a language I think you should use verbs like "estudiar" "hablar" o "practicar" i.e.
Hace muchos años que lo estudié, pero no lo he hablado en mucho tiempo. (It's been years since I studied it, but I've not spoken it in a while)
Hace mucho tiempo que no lo hablo/practico. (It's been a long time since I spoke it)
You can also change the order of the sentence :
Lo estudié/hablé hace mucho tiempo
Estudié español hace mucho tiempo.