Officially, everyone in PRC speaks Mandarin, properly putonghua. That is because school, etc., has been in that language since the 50s. Practically speaking there are modern variations, but not much different from English, is it varies from the deep South in the US to Scotland. Dialects are starting to come back but not for official use.
I found German pretty easy, Chinese almost as easy, Russian pretty difficult, and Japanese fairly hard. Others rank them in opposite order. It depends on something, but I don't know what. I