See there will be not much of a problem regarding the language or understanding it, but you may get confused with the terminology. So if you wish to appear for the NTSE examination, then I would recommend you to start reading the NCERT examination and then you have to focus on the terminologies first. For example, as per your surname, I guess you are from bengal. So if you are a bengali medium student then what you tell 'Upapadya' in Mathematics, turns to be 'Theorems' in English. So you need to focus first on the technical terms, for that you can refer to bengali books and as per your ease, you can write the terminologies in bengali. If you are from other native language, then you can follow the same procedure in your own language. This is the one and only way & the main thing that matters is the knowledge you have. So if you can acquire knowledge then the sources/books/languages don't matter. So keep on studying and don't think of it as a hurdle instead keep on reading as it is, and slowly with time you will understand.

For the NTSE preparation tips you can follow:

https://school.careers360.com/articles/ntse-preparation

I hope this helps. Have a great eve!