In current version of rdesktop there is a bug - when you trying to change input language via alt+shift (for example) something goes wrong and you can't write anything. I can use rdesktop only if i run it with -k en-us option and when in X input language is English. When input language is Russian i can not print some symbols from keyboard, for example . and ,. Also something wrong with ". To print this symbols i have to change input language to English, enter needed char and then change language to Russian. This trouble is at least in version 1.6 from ubuntu repository.
I hope you will fix this bug! Thanks for your work!