Hello,
.
Yes, you can do your preparation and attempt the examination in any of the language you want.
.
If you want to prepare in Telugu and attempt exam in English,then choose telugu books and while applying for examination choose English language and optional language as Telugu.
.
If you want to prepare in Telugu as well as attempt examination in Telugu then choose telugu as language and other language in optional.
.
Point to be note is, doing law in English has more value and have more job opportunities when compared to any other languages.
.
Best of luck