Your L2 figure for Zulu is not explained. You just seem to pick a figure of 15700000 without any basis. You do not quote any references as well. Also consider adding a language called Nguni. Remember Zulu, Xhosa, Swazi and Ndebele are part of the Nguni group. Your L2 figure might be explained by that you consider all Nguni speakers to be L2 Zulu speakers. That is not the case.