Switch update_plugin_messages.py to Python 3
scripts/update_plugin_messages.py is used to extract the messages (creating the catalogs) from all the resources other than the main GUI app. It is also called by
Messages.sh, which is the way messages are extracted e.g. by the KDE translation infrastructure (scripty). Python 2 is EOL already, so one of the planned changes is to switch all the helper scripts used by scripty to Python 3. This includes anything invoked in
scripts/update_plugin_messages.py to Python 3. Python 3 has been around for many years already, and available in stable releases of distributions for a long time; hence, IMHO a switch to Python 3 exclusively instead of making it work with both versions is better, and will avoid extra compatibility code all around.