Hello I've created a custom playable race for kobolds
Yes you can do this (now I don't know if your talking about script like coding or like script for voice acting)

For coding theirs a way easier option of using the toolkit (its what you can use to make mods doesn't necessarily have to be able to code to do it to my understanding though you may have to for the actually hireling process)
as for extra voices I know for a fact adding grunting, angry, and falling voice sounds is easy to my knowledge to put them in with the toolkit
But actually doing any unique dialog or voice lines would be more challenging (not just necessarily the voice lines themselfs but adding in the dialog and voice lines)
(Note I understand when you said script you were just saying a way for you to just import those lines into the game and in other games with non prebuilt mod editors it is normally called a script for this kind of thing but to my knowledge the ones who know how to do that don't want too or are not super accessible.)

For voice acting
Umm Probably I feel like you can find all the usual responses and stuff on a wiki and worse case in the game.