Languages of Theros

Language	Common Speakers	Comment
Common	Humans, Hags, Sirens, Gogons, Harpies	Standard Language
Leonin	Leonin, Tabaxi	Standard Language
Minotaur	Minotaurs	Standard Language
Sylvan	Centaurs, Satyrn, Nymphs	Standard Language
Giant	Giants, Cyclopes	Standard Language
Primordial	Tritons (Aquan)	Exotic Language
Silumas	Gorgons, Naga	Exotic Language
Sphinx	Sphinxes	Exotic Language
Celestial	Archons, Demigods, Gods	Mythic Language

Celestial, the mythic language of the Gods cannot be chosen when you are asked to select a language. Furthermore, Comprehend Languages, Tongues, and similar spells and items do not work on Celestial. Only very few mortals called Oracles speak Celestial. Only Oracles are able to understand the will of the gods.
On Theros, Dragons are not intelligent, majestic creatures but rather large fire breathing beasts. They do not speak any language. Replace draconic with sphinx if you have draconic as a language.