D&D 5E Best Languages For Arcane Research?

[Aquion]

I'm working on a new character who will be a Priest of Mystra. He'll start out as a Knowledge Cleric and then go all Wizard. As a human he gets Common plus one language. Knowledge Cleric gives him two more languages. The Faction Agent (Harpers) background will give him yet two more languages. What languages would you argue are the most important to Arcane Studies?

i think Elvish and Gnomish are obvious choices. What else?

 

[The Grassy Gnoll]

Celestial and Infernal

 

[EdL]

Dwarven if he's going to run into any runes.

 

[Boneguard]

Draconic as Dragon are creature of Magic.
Sharn could be interesting also.

 

[Curmudjinn]

With him being in the Harpers, having varied languages can be very important, depending on his role within the group.
I'm with Boneguard on taking Draconic. If memory serves, most magical writing is done in the Draconic alphabet, so that is a necessity for magic research and study. Since you are using Mystra/Faerun, some of the oldest(and strongest) magic in the world is from ancient Elven civilizations, so I would wager that is also a necessity.
I also agree with Grassy Gnoll about taking Celestial, to commune with your goddess and read her text. Infernal may be useful, but that is truly dependent on the direction you take the character and not essential.
For a fourth language, I would take Netherese, the Thayan language(Illuskan?), or another dead magical civilization's language. A ton of strong, human magic comes from fallen Netheril though, so that's probably what I'd do as a follower of Mystra.
Netherese, Elven, Celestial & Draconic.

Gnomish is a good choice if the character delves into that, but again, not essential unless that is their direction.

 

[thalmin]

Due to their being one of the oldest (if not the oldest) races, I think studying Giant might reveal some of the lost secrets of magic.