[blackwhite67]

I know it was said somewhere that Voban never learned magic not because he sucked but because of preference or something. It was said in the anime, too. It's the same with Doni, he won't learn magic because he's a sword freak. You might think learning magic would be useful and logically that's true, but these guys wouldn't be Campione's if they relied on magic.

Spoiler for Voban:

Voban spoke with perfect Japanese as he downed the cup of sake by himself, looking over the typical but undistinguished menu listing items like tempura and sashimi.
Until the previous day, this old man had no knowledge of the Japanese language.
However, both Campiones and accomplished magi possessed exceptional language learning ability. As a result, it was not surprising that Voban had mastered the language simply by conversing with Liliana who excelled in Japanese.
Furthermore, it only took him about fifty to sixty minutes.
Learning an unknown language in such a short time would not have been possible for Liliana. Likewise, even other Campiones and Great Knights would probably fail to match such a feat.

Voban didn't learn Japanese quickly just because of the large amount of magic he has.