Hi there

In response to your query, the official form which has to be filled for the examination does provide you the language to give the exam in, if you filled English as your medium of language then that would be followed in the exam. However if a correction window is still open to change the form then you do the same or if it's a computer based examination sometimes there is an option to change the medium of language, but that would really depend on the examination you would appear for and the candidate should watch out for changing the language while reading the instructions for the question paper.

Hope this answer helps; best wishes