Unclear step to generate a dictionaries

[AndresMpa]

Please write a foolproof "How to"

This line of code is not clear enough to me:

aspell -d <lang> dump master | aspell -l <lang> expand > my.dict

I' m not common with aspell What is "lang"? Also, How can I list the avalible one I have in my OS?

Each time I use the command I'm getting an error that says:

Error: The file "/usr/lib/aspell-0.60/en_US" can not be opened for reading.   # What I understand as a permission error

But, in a docker container I made I get the expected long list of words from aspell

[uga-rosa]

Look at the official aspell documentation. This project is not aspell. GIYF