Unable to download subtitles from every language

[Bigemul]

Describe the bug

I get:
udemy-dl.py: error: argument -s/--sub-lang: expected one argument.

While downloading, I used --sub-lang but it also works with -s without argument.

To Reproduce

python3 udemy-dl.py my_course_url --chapter-start 1 --chapter-end 5 -k cookies.txt --sub-lang

Expected behavior
I would like to download every subtitle.

Python Environment (please complete the following information):
I just manually updated everything in the requirements.txt file.
I didn't update python since I already have 3.8.3 and I saw someone with m3u8 issue (solved?) with an updated version of Python.

[r0oth3x49]

@Bigemul you can now use -s all as switch to download all subtitles.

[RiseT]

@r0oth3x49 I guess the docs should get adjusted then, as they don't mention "all":

Download specific subtite by using language code such as (en, es) if lang switch is not specified then default will be all subtitles