Add language information

[thebooort]

While most books are in english, most of them can be found in other languages or aren't even translate into english. So adding this information could be useful

[clizano]

How do you want to add language data? Can be a new column on raw_books.md?

[thebooort]

I prefer a new column in the csv file:
just add:

title, author, language

at the beginning and then write them. If you add more than one language, pls separate them with spaces:
i.e.

english spanish

I can easily generate the md with a script after that :)