[Baertram]

I like the idea and as the popup won't show very often (or not at all if users keep their addons updated and addon devs are able to do the same ) I guess the users won't complain.

German translation:

if language == "de" then
        return {
            TITLE = "Veraltete Addons",
            DESC = "Vielen Dank für die Nutzung von Elder Scrolls Online Addons\nEinige deiner Addons scheinen jedoch inzwischen veraltet zu sein\n\nVergiss nicht diese zu aktualisieren!",
            NOW = "Aktualisieren",
            LATER = "Später",
        }

If the button text "Aktualisieren" is too long then just use "Update" as well.