Obligatory "my answer does not constitute legal advice"; Skyrim, and by extension, the dragon language, is intellectual property of Bethesda.

Commercial use of the intellectual property - such as selling t-shirts that say "Fus Ro Dah" - would be violating their copyright. You're fine making Youtube videos that feature the language. 

Gotta disagree at DaanKaalZaal - you cannot copyright a REAL LIFE language that would be silly.

But a conlang is made up by a few people entirely, it is their invention and thus, it is their intelectual property. Just like if you make a song - you cant own a copyright for tunes, instruments or melody per se but you can own copyright for the actual piece created.

As I know, The Elder Scrolls own this Language. They are the one who made this language

@DaanKaalZaal: You can however own a language as intellectual property. Thus, like Paarthurnax pointed out, you can not try to make money off of said intellectual property legally without consent from the owner. 

Source: My lawer friend.

You cannot copyright a language.