I have one classmate and he is from Nigeria. He is so helpful and supportive person in my whole class. Since I'm new here and my Nigerian friend guides me with everything. I have a good friendship with him, but the problem is, most of the time I can't understand his English accent, but I never show and I never tell him that your accent is a little difficult to understand.
I wanted to know it is okay to tell someone that I can’t understand his/her accent and he/she must speak slow when speaking with me.
I am a little scared to tell him that he may be dislikes my comment.
Be polite and honest, if necessary say you often have problems when people have a strong accent, and say you hope they don't mind if you don't quite catch what they are saying and ask them to say it again.
I presume you are both speaking English as a foreign language. It's quite acceptable to ask him to speak a little clearer or more slowly. Don't criticise his accent, you will have one too, and maybe he is finding it difficult to understand you also.