The startup prompt, the Check for Updates result card and the messages the Updater puts in the
prompt were English whatever the app's interface language (storytold/wordcraft#5257).
`StartupPrompt`, `CheckResultDialog` and `Updater` get `with_translator(Translate)`: a
`fn(&str, &[(&str, &str)]) -> String` that gets the English text (the key, as in the craft-i18n
catalogs) and its `{name}` values, so translations may reorder them and an app on craft-i18n
passes `craft_i18n::fmt(i18n.t(lang, text), args)`. It is called when the card draws, so a
language change shows on the next frame. Buttons are looked up in title case and drawn in
capitals, so the apps' existing button rows serve. Without a translator nothing changes.