Rdesktop shows message: Warning no translation for key XYZ

If everything is configured correctly, you will never see rdesktop warnings about not able to translate unknown keys. Such a message implies that there is a possible mismatch between your keyboard layout and X-Windows or the chosen keyboard layout using rdesktop.

In our test we use the Mandrake Configuration tools for setting the correct keyboard layout for X-Windows. However, it is also possible to use Gnome of KDE configuration tools for settings the keyboard layout. Other distri might have other solutions for fixing the keyboard layout of your X-Windows.
Whatever tool you use to set the correct keyboard layout, verify the keys using an editor like KWrite. Just to be sure, restart your X-Windows after changing your keyboard layout (ctrl-alt-backspace in some distris).

A mismatch between your keyboard layout and rdesktop implies that you have the wrong keyboard parameter after the -k option, OR, you have an old rdesktop version with wrong or incomplete keyboard layout files. Try to upgrade to the latest version of rdesktop.

See Non-US keyboards on a Linux client using RDesktop Rdesktopfor all the details on how to configure keyboards on Windows and Linux.