@@Poly Lingua, it is shown that ponies speak English in the show, or some unified language. There are also multiple "dialects" from different regions, the only three being the normal one, the Manehattan one, and the Appleoosan dialect. They could have different conjugations/ways of saying things, but it shows in the show that different regions' ways of speaking are not that different. I like what you've done with Terrequian, Pegasian, and Unicornish.
In the show, it is also shown that Yaks have their own language/use a very primitive version of Equestrian and that Cows speak fluent Equestrian. If you could add words imported from Yak language or any primal language, it would be great! Anyways, I'm not a professional linguist, so pardon my misunderstandings of linguist vocabulary.
Overall, the language is nice (BTW, are you working on normal and abnormal nouns/verbs?). Also, how about the writing? We haven't really seen the written language in Equestria, so I suggest you use pictograms as Equestrian Characters.
(LOL sorry if I'm being pesky, nice job on the language so far)