452984: DynamicNls is slow if text key does not exist 

Change-Id: I51e9990629d920438ad403e8804db4a8542889f8
Task-Url: https://bugs.eclipse.org/bugs/show_bug.cgi?id=452984
Reviewed-on: https://git.eclipse.org/r/36906
Tested-by: Hudson CI
Reviewed-by: Andi Bur <andi.bur@gmail.com>