Issue #2219499 by Berdir, alexpott, Gábor Hojtsy, vijaycs85, swentel: Generalize language config override responsibility.

Issue #2098119 by beejeebus, alexpott, chx: Replace config context system with baked-in locale support and single-event based overrides.

Issue #2162013 by alexpott, Berdir, sun, pwolanin: Critical performance regression due to config schema + TypedData lookups in installer.