See, I'm actually OK with it being Hindi. Its the language of the Gods, yeah. So for those of us who play Skyrim, so were the Tha'um. Being fluent in the Dragon Language was lost or entirely unknown. But one or two words... quite possible they would have survived. And have power, at that... of course, I assume part of the essence of the unicorn horn was used up doing that little teleporting trick. Anywho, I vote Yes to the him using the Hindi, but maybe keep it shorter. And VERY limited.
Arcon is God of Locks, Doorways, Barriers... as well as everything they encompass (Keys, Restraints, etc.). This is to say both physical and metaphysical in concept. Yeah, he's the god of that doorframe over there. But he's also the Gatekeeper between the Astral and Equestria. He prefers using physical things for his work though... far easier to work with.
Mmm, technically all teleportation is within his domain. Doors and all that jazz. Regular unicorn teleportation, very small scale and doesnt even show up as a blip on his radar. However, Unicorns don't really use it to travel very far. Several hundred feet, maybe a few thousand. But generally speaking, small scale. The little trick you just pulled, with the runes and the horn, AND the language of the gods? Travelling quite a few miles? That's totally gonna ping him. He won't know what or who it was... but he's gonna know where it went and where it came from. Might catch his interest...