"Yo mama" jokes are considered funny in some parts of the world outside the United States, including Europe, Australia, and parts of Asia. Most cultures find the jokes funny when both parties realize the insult is meant as a joke.
It's best to avoid using "yo mama" jokes until you are sufficiently familiar with a culture. For instance, many people from eastern and south eastern Asia will not find the jokes funny. The role of the family in these communities differ from that in the United States in such a way that some people may fail to see how the insult might also be funny. That said, most other countries outside the United States have some version of the "yo mama" joke.