How many Languages are there in Equestria?

[Gaines 1,223]

Not counting English and other actual languages the show was dubbed in. So far, I only know about Ponish and Old Ponish. 

[Batbrony 16,055]

This is one of those questions that, unfortunately, is kind of impossible to properly answer unless the show writers were to (1) get more specific or (2) actually explore the linguistic history of the setting and various cultures.

 

That said, it is a question that fans are more than free to have fun with in their own fan art, particularly in fanfiction.

[Splashee 28,564]

While in its hayday (pun intended), the show's staff should have created a new language like Klingon for Star Trek.

[FlitterFlutter 1,583]

As far as we ever know all sentient beings in Equestria speak the same language. Even when they left Equestria in the movie adaptation they could still understand all the creatures easily.