Fixed language path for languages with non-URI chars

This PR fixes issue #2070: Incorrect links for languages with non-URI characters. I'm not a Ruby developer, so I'm not sure if I have structured the code correctly.
I have led you astray! What I told you to look for works... but there's an easier way.

`submission.problem` has several methods: `track_id` gives you the language slug, `slug` gives you the problem slug, and `language` gives you the name of the language.

I'm so sorry about this!