Wow, I've never heard of such a long process to save a locale file -- we've used the current version of the translator plugin a few times, for OMP 1.2 and OJS 3.0, and so far it's been OK.
@mtub, have you heard of performance issues? Perhaps with large locale files?
I know that certain file-intensive processes take much longer on Windows machines compared to Linux/MacOSX ones (e.g. the installer), but this does sound exceptional.
As I recall, the spinner corresponds to the "save" request, so I would expect the spinner to stop only when the changes have been saved. This is something that you could confirm with a developer toolbar like Firebug, which can show when operations are in progress.
If you're doing large amounts of work, have you considered working with the XML files directly? That may be less painful than working through a web interface of any sort. As far as I know, we have translators working using both methods -- but again, @mtub may be able to confirm.
Public Knowledge Project Team