Romulus, Vulcan, Kronos, Orion,... and many other examples in the Star Trek universe. Is there a reason why they all have names from Roman and Greek mythology? is there a reason for that ? Are they just using Federation (human) designations when in fact they have different names in their respective culture's native languages?
Many of the similarities in names can be put down to the viewer only hearing the Earth name for their planet and species. Per Memory Alpha:
The Worlds of the Federation (p. 18) gives T'Khasi as Vulcan's indigenous name and states that Terran astronomers, taking inspiration from Terran mythology, provided the planet with its name of Vulcan, which the Vulcans gracefully accepted as the planet's official Federation designation.
It makes sense. Suppose we did find sentient life on the planet Mars tomorrow. Would we call them Fshdyf'ahgjio'FG? Or Martians?
Even thinking in terms of Earth languages, people rarely refer to the Française, we just call them the French. There's no social expectation that foreigner are named in their own tongue (and indeed, Spock mentions that even his own name is unpronounceable to humans).
Presumably Vulcan was named by Earth astronomers for its barren, hot landscape. Romulus would be named for its close proximity to Remus, the other planet in its system. Orion presumably orbits one of the actual stars that make up the constellation Orion (whose scientific names are Alpha Orionis, Beta Orionis, and so on).
The name of the Klingon homeworld is technically Qo'noS, not Kronos. Presumably we're made to believe that in-universe, it's coincidental that the pronunciation is so close to yet another mythological figure.
According to Star Trek, Olympian Gods are actually aliens who traveled to Earth in ancient times which resulted in the Greek Mythology we see today. In Star Trek: The Original Series S02E04, Kirk and the crew even met Apollo (Son of Zeus) on Pollux IV.
It's very much possible that Olympian gods (and, other gods from different mythologies) have influenced lots of different alien cultures across the cosmos. So, it shouldn't be surprising if we see alien planets having name from human mythology.