One adj. word for "have never been used before"?
There are a few alternatives involving prepositions:
I am unfamiliar with / illiterate in / ignorant of / incognizant of / inconversant with this programming language.
As mentioned, unfamiliar can also be used directly as an adjective applying to the programming language. The "to me" is then implicit in the meaning.
unfamiliar - This is an unfamiliar programming language to me.