[BUGFIX] Fix language label

Use the core "language" label for the sys_language_uid field

Change-Id: Ia94d870f22be42998e5465d2187719079daab004
Reviewed-on: http://review.typo3.org/32182
Reviewed-by: Tim Lochmüller <tim@fruit-lab.de>
Tested-by: Tim Lochmüller <tim@fruit-lab.de>