How to say "to know" a language?

Question

I ran into the sentence in Duolingo:

本当に? 弟も中国ができます

which I was supposed to translate as:

Really? My younger brother also knows Chinese. 

I was a little rusty about the usage is "ができます" so I ran it through Google and Deepl, but neither translate it that way.

Google translates it as:

Really? My younger brother can also go to China

and Deepl translates it as:

Really? My brother can go to China.

Have to say, I've not been impressed with Deepl lately. I don't have to be an expert to know that it missed the usage is も.

I thought the できます meant "can"? Why wouldn't Duolingo use を知っています for "to know" a language?

Which translation is correct? Or are they all wrong?

Answer 1

Normally, in Japanese one doesn't literally "know" a language; we use other verbs to express this instead. The English idea of "knowing" a language is actually a bit strange - or rather, the English verb "to know" is broad in a way not seen in many other languages. It's not as if the English language could be turned into a question, such that an English speaker knows the answer to that question.

(Aside: The 知っている/分かる distinction is not unlike savoir/connaître in French or wissen/kennen in German. And yes, 知っている isn't a plain form, but the reason why we don't typically use 知る is a whole other story.)

できる is a common choice. It's used as the potential form of する "to do"; so it sort of means "to be able to", "to be capable of" etc. (Yes, it's irregular - rather, it's a suppletion.) But it's a real verb, not a modal like the English "can"; the thing that "can be done" is typically (but not always) the grammatical subject; and that subject can be an ordinary noun. So 中国語ができます -> some action involving 中国語 is possible.

Of course, as Gui Imamura pointed out in the comments, it's also perfectly fine to say that you 分かる (understand) a language, or 話せる (can speak) it, etc.

Answer 2

I think the most common, general, and natural phrasing is

中國語ができます . . . I can speak Chinese.

I think 「. . . が話せます」requires a bit more context:

Q: "何か外國語を話せますか？"
A: "中國語が話せます。"

On the other hand, 「中國語を知っています」 would require a narrower context. For example,

Q: "Can you speak some second language?"
A: "中國語を少し知っています。" . . . I can speak Chinese just a little.

because you hesitate to say 話せます. That is, 「話せます」and「できます」imply that you can speak it adequately. If you aren't confident, you resort to 「少し知っています」。(But, at the moment, I can't think of a context where「知っています」 without 少し is appropriate.)