Roughly speaking, it says 'Can you speak Japanese?'.
日本語を話すことができるの?
日本語を話せるの?
These are better but you may be talking to a native speaker...
I would suggest 『日本語は話せますか?』
The first usage is far too casual, and the second actually expresses surprise that the person can speak Japanese.
"できる" is also a verb meaning "to do." You don't "do" a language, you speak a language. So the verb choice here is a bit odd as well.
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