{{msg-mw|Fogg-installed|notext=yes}}

What's the function of the comma here?

Changed to a . with mwr:66461. Compare with fogg-not-installed ("Firefogg is not installed or not enabled.")

I think that may be wrong, Raymond. I think this may be the first part of a two part sentence. Have you check the JS source?

If there's supposed to be a dot, then of course the translation is easy. But if a comma is used, then it's more difficult and it would be good then to possibly do it differently, because you can't assume that everywhere where you use a comma in English, the respective separator is also used in other languages. For example, in English it's possible to put a comma before "and" or "or", but in German this is very uncommon.

I've added this question to a few other questions on Mdale's discussion page.

Hmm not checked, but now. And it seems unused. Maybe doublecheck because I am not very familar with JS

Not used indeed:

mw.Firefogg.js: "fogg-installed" : "Firefogg is installed.",
mw.Firefogg.js: "fogg-not-installed" : "Firefogg is not installed or not enabled.",
mw.Firefogg.js: // CSS selector for the "firefogg is installed" message div
mw.Firefogg.js: 'target_installed': false,
mw.Firefogg.js:                 gM( 'fogg-for_improved_uploads' ) + ' ' : gM( 'fogg-not-installed') + ' ';