I'm using the Locale.available property, and it seems the locales are always generated:
Generating locales (this might take a while)...
en_GB.UTF-8... done
en_US.UTF-8... done
en_ZA.UTF-8... done
Generation complete.
onyx.fusionapp.com en_ZA.UTF-8 locale generated ... done
Generating locales (this might take a while)...
en_GB.UTF-8... done
en_US.UTF-8... done
en_ZA.UTF-8... done
Generation complete.
onyx.fusionapp.com en_US.UTF-8 locale generated ... done
I inspected the definition of the property, but I'm not sure where the bug is. Should fileProperty with identical contents be causing onChange to trigger?
What seems to be going on is, /etc/locale.gen is changed, uncommenting the line, but then the dpkg-reconfigure locales rewrites the file with the same set of locales enabled but a different set of lines and comments. So, next time the property runs, it wants to change the file again.
I changed it to run locale-gen instead, which avoids the problem.