Issue #1987726 by vijaycs85, disasm, YesCT, pdrake, tstoeckler, dawehner, Xano, likin, stella, andypost, prateek479, Gábor Hojtsy, kgoel: Convert language content page related callback to new style controller.

Issue #2239065 by tim.plunkett | webchick: Overridden config bleeding through to configuration forms.

Issue #2203407 by nod_, sun: Replace #attached library array values with provider-namespaced strings.

Issue #2165155 by Berdir, tim.plunkett: Change $entity_type to $entity_type_id and $entity_info to $entity_type/$entity_types.

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

Issue #2005716 by tim.plunkett, msonnabaum, dawehner, alexpott, effulgentsia: Promote EntityType to a domain object.

Issue #2084279 by herom, andypost, David Hernández, dawehner, Xano: Remove plugin.manager.entity service in favor of entity.manager.

Issue #2066535 by tim.plunkett, jsst, Berdir: Add EntityManagerInterface and stop typehinting with EntityManager.

Issue #2089627 by tim.plunkett: Move \Drupal\system\SystemConfigFormBase to \Drupal\Core\Form\ConfigFormBase.

Issue #1978916 by likin, YesCT, disasm, ayelet_Cr, tim.plunkett, vijaycs85, Letharion: Convert locale_translate_page() to a Controller.