While there may be lots of copyright issues and the publisher will likely need to be contacted. I think starting with the author is the way to go. The email can be rather simple and the content of your question is a good starting point:
Dear X,
I would like to translate your book. I am not doing this for financial gain. I want students in my country become better familiar with the topic.
You may want to include a little about yourself so the author realizes you are familiar enough with the material to translate it and have a use for the translated book.