Russian is certainly not easy but I learned the alphabet in one day.
Chinese requires memorising 3000 characters to be basically literate. University graduates will know around double that.
Chinese is very difficult to learn particularly because of the tones, but also the grammar is very different.
It is generally agreed that Vietnamese is one of the most difficult for European language speakers.
The easiest for all speakers are languages which are closely related, so other European languages for English speakers.
As for gender, most languages have gender differations. Old English did. Chinese doesn't.
Latin has three genders as do many. Kivunjo - an African language - has 16.
