FuBar_BabelFu\FuBar_BabelFu.lua:26: attempt to call global 'GetNumLaguages' (a nil value)
It's a simple fix. GetNumLanguages was spelled incorrectly prior to 2.4 as GetNumLaguages (as shown in the error you encountered). Simply find and replace all instances of GetNumLaguages with GetNumLanguages within FuBar_BabelFu.lua and everything should work for you. Maybe someone with SVN access can correct this small bug. Please note, I have not tested this yet as I don't currently have access to the game, but this should most likely correct the problem.
EDIT: Please disregard as it appears someone has already corrected this bug.