If you connect to a from a client that has localized keyboard (eg: ubuntu with italian keyboard) to an RDP server that has only a local layout keyboard installed (eg: only italian) the keyboard layout will be a mix of italian and english (unusable).
to solve this I succeded in this way:
If you add the EN-US keyboard to that RDP server (under Keyboads and input methods: example window here ) you will get the client layout (eg: italian) working correctly wile using rdp connection through guacamole.