Added es version of language_modeling.mdx doc
# What does this PR do?

Fixes(#15947)

Added spanish version of language_modeling.mdx documentation file. 


### Before submitting

- [X ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).



@sgugger 


_The documentation is not available anymore as the PR was closed or merged._<|||||>@omarespejel Could you confirm this is good to merge?