Question: I am collaborating with a foreign author. As I am still pursuing my degree, I have to add my supervisor's name in that paper, even though my supervisor has not contributed to the preparation of this manuscript.

How should I ask my collaborator (foreign author) to include my supervisor's name as a third author? I need some help in this. 

**Edited:** As my supervisor has told me to add his name, I am obliged to add. I have no other options left. I am asking how should I write and request to my collaborator to include my supervisor name in the manuscript. Also, I am afraid whether my collaborator will feel odd or bad if I request him to do that.

Please help me: what should I say to my collaborator so that he may give third authorship to my supervisor?

Answer: 
Like many questions from graduate students, I believe a possible answer to "How should I write and request to my collaborator to include my supervisor's name in the manuscript?" is "Ask your supervisor.". 

The question to ask is something like this: "I'm about to write to Foreign Author to get your name added to the paper. What should I list as your main contributions to it?"

If the collaborator finds the result reasonably convincing, the supervisor's name gets added. If not, it is not your fault.
After you have asserted that your supervisor really merits coauthorship, you could simply write to your collaborator:
"dear collaborator, could you please add [supervisor name] as coauthor? [supervisor name] has contributed to the research in this and this way. Thanks!"