I know this is a very old question, but I just happened to find the solution:
a registry key exists for that very problem
To change the default behavior to obtain the Default input language setting from the default user profile, you must set a registry entry value on the terminal server. To do this, follow these steps:
- On the terminal server, click Start, click Run, type regedit, and then click OK.
- Locate and then click the following registry subkey:
- On the Edit menu, click Add Value, and then add the following registry information:
Value name: IgnoreRemoteKeyboardLayout
Data type: REG_DWORD
Value data: 1
When the IgnoreRemoteKeyboardLayout entry is set to 1, new user profiles inherit the Default input language setting from the default user profile that the user account uses.