I don't use it and wouldn't mind freeing up the space, if I delete it but want it at some point in the future, could I download it again for free? I didn't pay for it, it came with my mac.
Yes you can. Delete it now and download it later. Or you back it up.
Also know, that GarageBand has an extra folder in the Library / Application Support folder with samples.
To get rid off languages, use Monolingual.