There are no such rules about the compulsory indian language paper. You can select any language as your compulsory elective provided the paper you are choosing must be known to you. This is because if you enroll for a new language and try to learn it then you have to devote more time to it and as a result your preparation of other GS papers may get hampered.

So I would say you can choose any paper but its better to choose a language which you know and you can read and write the language fluently.

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https://competition.careers360.com/articles/how-prepare-for-upsc-ias

I hope this answer helps. All the very best for your future endeavors!