I needed to do this and since saving as CSV is not supported and HTML is not attractive for large projects, I chose TMX. I guess that I could have imported the resulting TMX to a new glossary??? And then open that in Excel to take out the source column. Anyway, I opened it in my text editor and via Find and Replace and sorting, I extracted the source. Removed the duplicates, quickly translated the resulting small file, imported the project to a TMX. Used that for translating the huge Studio. Why all this hassle? Because I often have problems with propagation in Studio projects (and only there) must me something in my settings :(.