First of all, split all your pro files into pro and pri files. Then put all the pri files in one global pro file and generate the language file for this pro file.
The special pro pro file is as follows:
TEMPLATE = app DEPENDPATH += Proj1 Proj2 Proj3 include(Proj1/Proj1.pri) include(Proj2/Proj2.pri) include(Proj3/Proj3.pri) TRANSLATIONS = en.ts fr.ts it.main.ts ja.main.ts nl.main.ts
A script can easily generate this project language file for you.
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