If I recall correctly, the GBA games weren't localized because Capcom didn't think there would be a market for text heavy games like Ace Attorney in America on the GBA. When the DS came around and opened the door for more potential players beyond kids to experience portable gaming, they figured it would be the perfect opportunity to bring the series over.
As for the second question, I'd assume so. The JP releases of the DS ports actually let you switch between Japanese text or the localization, despite the JP releases usually being released a few months ahead of time of the localization.
I actually ended up buying the GBA games just for the novelty. Funny thing is that if insert one of the GBA games in the GBA slot of a DS while playing the corresponding DS port, every case in the DS port of said game gets unlocked. Always thought that was kinda cool.