How they have been exposed to the language matters.

Written and read languages you are most likely to gain through traditional teaching. Spoken languages can be learned via subtitles on video media.

Even then spoken breaks down further. Someone will learn to understand spoken English before they are comfortable speaking it themselves.

For me learning Swedish I learned to comprehend speech, then to speak, then to read. My written grammar is still poor 15years later because I'm very rarely called to write the language.