Hello all, thanks for your replies and sorry for my delay .
I finally did it work, but don't remember how. What is for sure is that I re-configured the .pro file adding the debug_and_release option, and configured it to put the resulting apps into diffrent dirs with the following code:
Qt Code: 
  1. CONFIG(release, debug|release){
  2.    DESTDIR = release/
  3.    TARGET = designer }
  4. else {
  5.    DESTDIR = debug/
  6.    TARGET = dbgDesigner
  7. }
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Also I copied the translations/ directory to debug and release folders to avoid doubtsa bout problems loading files, or different versions of translations. I also changed the line that john_god details above. I guess all that did the trick