Thanks for your really fast reply !
What is the installation directory ?
It's not the home directory (e.g. ~/.qcad), isn't it ?
In my installation, everything seems to be in /usr/local/share/qcad/ : fonts, libraries, patterns, plugins, scripts, ts.
Fonts and libraries apparently work ; I don't know for the plugins, scripts, ts. But the patterns files are not found by the GUI.
Finally, what should I report exactly ?
Can I test something (move files to the right location) ?