Role of language in Descriptive paper
It is a misconception that any particular language will fetch you a good score.
It is the knowledge about the given topic and the way you represent that knowledge that will help you score more.
The thing that works for everyone is his strength. If he writes an impressive letter/essay of appropriate words with correct format and accurate points he will definitely get a good score.
Yes, command over the language you are going to write your paper is definitely a deciding factor.
So, choose the language you have a good command of and you are confident enough to represent your thoughts and data on a certain topic.