I have the problem, that with activated "show learnable next" only completely new spells are shown. E.G. for my 67 priest only prayer of mending at 68 is shown, not the other spells, that will have maybe a new rank at 68. Same issue for my lowlevel druid, showing me no new rank-spells, but a completely new spell like innervate. I use the german client for my wow.
The line 55 in the file TrainerFu_VisitTrainer.lua must be changed as follows to work i. e. with the german client (The string Rank should be replace with Rang):
if skillRank and string.find(skillRank, "(Rang%s%d)") then
Therefore simply offering the possibility to translate this in TrainerFuLocals-xxXX.lua. The same exist already in DemonTrainer.lua, but it does not seems to work with the remaining skills.