You are right, this option is not available in Trados 2009.
But, actually "allow multiple translations" is enabled by default in Trados 2009 and you don't have a chance to modify it.
Even if don't use CTRL + SHIFT + U to add a segment as a translation, the multiple translations will be updated to the TM when you use "Batch Tasks->Update Main Translation Memories".
Kay Barbara wrote:
I would like to create a TM that allows multiple translations for identical source segments in Studio 2009 SP2 (9.1.1264.0) but I cannot figure out how to do this. I think I remember that this option used to be available in older Trados versions but I can't find it now. Any help greatly appreciated.