Eskimos use at most 12 different words for snows,which is not many more than English speakers and should be expected.

= Eskimos use at most 12 different words for snows, and the figure is not many more than (what= the words that) English speakers (use) // and (it) should be expected...

1, not many more than 因后面隐含的中心词是words，故用many. 这种many，是adj转adv的用法

2，为便于理解，than 一般都可看成是than what 或其缩合