People like to use Latin for spellcasting because it sounds fancy, but to those that spoke it it was just their language. They would have sounded like an anime character shouting the names of all the moves they use
Giga Terebro Confractus sounds like an incantation that'll summon a giant earth elemental or something, but it's literally just https://youtu.be/rpaTYemj6_I
You misunderstand. Its about Will. Speaking normally won't do anything. But speaking ancient dead languages helps drives that Will. Same reason you put up spooky decor and have moody lighting. The ambience helps the Will become manifest!