There are no certifications on a specific language. Instead, the certifications are on a specific technology, such as "Developing Web applications" or "Developing Desktop applications", regardless of the programming language that you use to write such applications.
At the beginning of the exam you are asked which programming language you wish to be used in the questions. This only serves to display the sample code; the questions merely ask which method or which class you would use to achieve a specific result. Such methods
and classes are part of the Framework Class Library, and they would be the same regardless of the programming language that you use for calling them. Therefore, the language that you choose for the exam is mostly irrelevant.
Note that some of the newer exams only offer the choice of C# or VB. The older ones also offered C++. Specifically, 70-548
is available in C++, as you can see at the beginning of the exam description:
http://www.microsoft.com/learning/en/us/exam.aspx?ID=70-548&locale=en-us
