According to the
Development page, translation (.po) files can be tested by running calibre from the command line from the same directory where the .po file sits... I've tried this and it doesn't work (it shows the unmodified strings, not the ones in the .po file).
Am I maybe doing something wrong? Some environment variable that might be disturbing it? I tried with 0.6.0 and 0.6.3 on two different linux machines.