日本語ができます or 日本語が話せます?
I've never actually had any particular lesson about this, but I always have seen people saying "日本語ができます", I actually saw in a Japanese book that this is an abbreviation of "日本語ことができます". However, I've always seen English-Japanese speakers saying "日本語が話せます". I already know that "話せます" is the potential polite form of 話す, but, is this actually a usual and natural way to say it or is it a translation thing? Which one is more widely used? Honestly, I've never seen "日本語が話せます" in real context before...

Question

日本語ができます or  日本語が話せます?
I've never actually had any particular lesson about this, but I always have seen people saying "日本語ができます", I actually saw in a Japanese book that this is an abbreviation of "日本語ことができます". However, I've always seen English-Japanese speakers saying "日本語が話せます". I already know that "話せます" is the potential polite form of 話す, but, is this actually a usual and natural way to say it or is it a translation thing? Which one is more widely used? Honestly, I've never seen "日本語が話せます" in real context before...

Answer

日本語ことできます sound incorrect, because there is no particle and particles are essential for structure and meaning in Japanese sentences.

"日本語を話すことができます" and "日本語を話せます" both have the exact same meaning, but the first one sounds more formal and polite. Generally, the longer you can make the phrase, the more polite it seems.

Also keep in mind that after the direct object in a sentence, you usually use を instead of が. が is fine to use, but it simply puts emphasis on the object.

Answer

Hola. 
日本語が話せます y 日本語ができます nos dan el sentido de "saber hablar / saber japonés" y ambas son correctas. También puedes decir 日本語を話すことができます. A veces, escucho que los aprendices dicen 私は日本語を話します, pero nos suena como "hablar japonés habitualmente / ser nativo de japonés". (*Está bien con más detalles como "en las clases / en la casa / cuando estar con los japoneses / en la empresa / etc.)

Espero que te ayude.

Answer

i think 日本語ことができます isn't complete, since you always attach こと after a verb to make it a noun. So I think it should be 日本語を話すことができます。But once again, it's too long-winded. So maybe just use  the casual form 日本語ができる。Personally I think　日本語が話せます　also works.