Accents would be too difficult. The English voice actors they hire would have to know how to do multiple different accents.
And as far as languages go, that would be too many voice actors that they'd have to pay.
At the moment, there are 10 voices for each gender in Character Creation.
That's 40 voice actors. 20 Japanese, 20 English.
If they were to add, say, French and Spanish, that's 40 more.
That would be 80 voice actors they'd need to pay.
Also, let's count the voices of the main cast.
There's 28 characters. However, 2 don't speak and 2 are alternate versions of main characters(Alpha and Omega).
So, that's 48 voice actors.
Add 2 more languages, that's 96 voice actors.
In total, they'd have to pay 176 voice actors.
That's twice the amount of voice actors they've already payed.
I think we'll have to settle for just English and Japanese.
Either that or have even less CaS voices.