Unfortunately, we don't know. Skyward Sword doesn't really have much voice acting in Hylian, so we just don't have enough data to say whether they actually made a language, or just a translation dictionary, or if it's just the few lines you hear in game declared to mean something specific.
Nonetheless, the answer is probably it's gibberish. (It's definitely not Japanese.)
There are four Hylian scripts. The first two, Old Hylian (Ocarina of Time) and Modern Hylian (Wind Waker), are just fonts for writing Japanese syllables. The second two, the Hylian alphabet (Twilight Princess), and the new Hylian alphabet (Skyward Sword), are just fonts for English.
All the text in the game is written in Japanese or English using these fonts. In Skyward Sword all the signs are written in English, or English-derived gibberish like 'mnop qrstu'. If they had created a language, or even a dictionary, they probably would've written something aside from the song in that language. There would probably also be hints of it in Hyrule Historia, and there are not.