I feel that trade goods buildings shouldn't be in the game.
AFAIK, they can't be (re)moved. If you build dimplomatic tralslators somewhere, then you won't be able to use that land square ever again.
They can be captured. It might appear to make sense, but think about it. How can you capture the right to distribute something (i.e. patent) through military action?
And they simply feel wrong. What exactly takes that square?
I think it would be nice if those buildings would "disappear" after you finish constructing them. Like Habitat improvement. That would make much more sense.