Dear,

MOSAI is probably one of the best Japanese language institutes in Delhi if you are looking for a professional Japanese course in Delhi taught by native speakers. Here are some more institutes to study Japanese in Delhi-

1. Nihongo Center.
2. The Japan Foundation.
3. Nihonkai Japanese Language Training Institute.
4. Tsubomi Japanese Language Institute.
5. Study Japanese in Delhi University.
6. Department of east Asian studies (Arts Faculty)

You can find more information about these institutes on their official websites.

Hope this helps!