No it is not legal. It is covered by CITES - the convention on international trade in endangered species. It is on appendix I, which means that all trade is illegal, so pets are definitely out. A quick look at the current conservation status shows that wild populations are decreasing and so they need to be protected in their natural habitat. These days a lot of people ask about primates as pets, but they really aren't suitable - they need a huge investment of time and money that most people don't have and even to get a licence for a legal species, you are expected to demonstrate the knowledge that requires years of experience and research to acquire. Finally, the illegal pet trade in primates ends up in the killing of mums to take their babies and is causing a lot of conservation concerns. It is better to have a domestic animal that enjoys being a pet and put your money into lemur conservation if you really like lemurs.