I always have trouble with editing math papers for publication. I know there are plenty of checklists for English exposition but is there one for math specific exposition errors?
In the same spirit as above: look at the video where Jean-Pierre Serre explains in English how to write mathematics - badly!
Often hilarious, but so true...
Steenrod, N.E.; Halmos, P.R.; Schiffer, M.M.; Dieudonné, Jean A.; How to write mathematics. American Mathematical Society (1973).