When I change the language on the touch keyboard (surface Pro 3 ) the language input changes correctly.
However when I change the language on the attached Surface keyboard the language input doesn't change.
Pressing the windows button and the space bar shows the language as changed, BUT it remains in English.?

Method 1:
To Change display language and input language
Follow these steps:
a) Press the ‘Windows + X’ key on the keyboard.
b) Type Control Panel and click on Enter.
c) Select Clock, language and region.
d) Click on Language, click on “Advanced settings” from the left panel.
e) Select the language under Override for Windows display
language and Override for default input method section. f) Click on “Save” button.

If the issue persists, I would suggest you to refer to the following article follow the steps to change the input method and input language and then check.
Add a language or keyboard
http://windows.microsoft.com/en-in/windows-8/using-multiple-languages
Language packs

http://windows.microsoft.com/en-us/windows/language-packs#lptabs=win8