I'm resubmitting this extension just because I'm not at all satisfied with the reason for its first reject (https://extensions.gnome.org/review/2743). A second reject would do.

Well, changing locale files is not that different from changing JS files in an extension downloaded from the net (because you still need that if you don't want Monday). And this affects gnome-shell only, other apps keep the wrong setting... I'm not really sure on this one, my feeling is that this is wrong, but generally we don't reject extensions on design principles...

Yes, you make a good point, and this is how I found it, searching through the js files that I downloaded from the net :D. I'll try to make a point too. I just installed thunderbird + lightning and evolution. Both offer a choice, indeed, any. Evolution even sets the start day differently, presumably based on the timezone info, certainly not based on the locale settings. I've double checked with Google and Yahoo, and sure, the start day of the week is customizable. In Google's calendar application too. Anyway, the point is that, even if it's wrong, it's less wrong than having to define a customized locale. I don't even want to attempt it since I'm sure I'll instantly forget how to do it again. The good point is that it's not necessary.

Ok, I'll approve this for now, but to make this extension worthwhile you should at least wire up a GSettings key.