A Land Far Away

It is my understanding that arcane magic is spoken and written in the draconic language.

What about divine magic?

It has been suggested that good/neutral clerics cast in celestial, evil clerics cast in Iifernal and rangers/druids cast in sylvan. But I think that was someone guessing. Other arguments in these forums regarding the invoking of a god's name would suggest that divine magic does not have a specific language... sort of like divine spells are merely answered prayers to a god... in that case, how do divine scrolls work? And how about scrolls for spells that are both arcane and divine and can be used by both types of casters?

also arcane doesn't HAVE to be spoken in draconic, it's simply a common practice

The "arcane language" (there's no such actual thing) was derived from draconic. That doesn't mean much, or all kobolds would be carrying spellbooks. No form of magic has an actual true language, those went out with 3e &D (although the language of illusions is still referred to in some older books I think).

That of course doesn't mean we can't use languages in magic. There is no fixed rule, so the "rule of cool" applies. I for one like seeing paladins chanting in celestial, druids murmuring druidic and clerirc chanting infernal. Or sorcerers with verbal components in common. It's all good.