Tacitus on historicity of Jesus - reliable source or not?

[The Mikado]

Of course, this could just be me not understanding which languages were prevalent in which areas of the Roman Empire. (if someone does have info on that I'd like to know about it)

The elites from the Western half spoke Latin, the elites from the Eastern half spoke Greek.  Indeed, most of the soldiers raised from the Eastern Empire would speak Greek and use Greek as their lingua franca, and colonial administrators would almost certainly be bilingual in Latin and Greek (as most heavily-educated Romans were).  Though Pilatus would've definitely had Latin as his native tongue, he would've been fluent in Greek and been able to converse with the Temple Priests and other Jewish elites in it (though it'd be very doubtful he'd know any of the Aramaic of his subjects).

[The Mikado]

To those of you who said no, do you accept what he wrote on other historical figures?

Not necessarily, any more than you should take "collapsable boats" Suetonius or "there was a magical tree at the fortress of Machaerus, I swear!" Josephus or any other classical historian at face value on everything.  For a Tacitus-specific example, he writes down Boadicea's death speech.  A death speech that literally no one would have lived to report and that wasn't given in Latin anyway and is almost certainly 100% fictional.

[The Mikado]

Just for fun, my all-time favorite passage from Josephus (and an example as to why you should take classical historians with a grain of salt):

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