I don't have a Windoze machine myself, so can't test there, but the readme for the Mac version does not say anything about it. There also seems to be no setting in the preference file for this (or at least none that I could find).

I searched the list-archives and the "best" instruction I found was to delete all .msg files inside /po, which seems a bit crude to me.

Is there a more elegant way to do this?

I understand from an older discussion that the assumption was that "non-technical" people were assumed to want to use Pd in their native language. I did installs this week on about a dozen machines and apparently they all belonged to "non-technical" people, even though every single one of them runs all software on their machine in English only... Wouldn't it be wiser to assume that whatever the language is that the OS is running in, is also the language that people really want to use their software in?

Just my two cents.