Issue #1862202 by plach, Berdir, katbailey, ParisLiakos, alexpott, chx, sun, larowlan, Gábor Hojtsy, cosmicdreams, vijaycs85, YesCT, penyaskito, andypost, Albert Volkman, joelpitett: Objectify the language system.

Issue #2061971 by naveenvalecha, herom, InternetDevels: Replace user_access() calls with ->hasPermission() in block module.

Issue #2028035 by vladan.me, ceng, Berdir, David Hernández, larowlan: Expand CustomBlockInterface with methods.

Issue #2145007 by tim.plunkett, h3rj4n: Convert form_set_error() in FormBase classes to use FormErrorInterface.

Issue #2102369 by vijaycs85, JeroenT, ACF, rteijeiro, -enzo-, tim.plunkett: Remove drupal_set_title in custom block module controllers and entitylist controllers.

Issue #2004244 by Berdir, plach, tim.plunkett, msonnabaum, das-peter: Move entity revision, content translation, validation and field methods to ContentEntityInterface.

Issue #1998658 by larowlan: Fixed Creating Custom Block with same name as existing block throws SQL error.

Issue #1983682 by tim.plunkett, h3rj4n, larowlan: Convert applicable custom_block_menu() entries to use _entity_form() in routing.yml.

Issue #1754246 by webflo, swentel, penyaskito, andypost, alexpott, YesCT, dagmar: Languages should be configuration entities.

Issue #2025991 by plach, David Hernández: Introduce hook_entity_prepare() to generalize hook_node_prepare().

This reverts commit c4e52bb6.

Issue #1620010 by dawehner, ParisLiakos, plach, jibran: Move LANGUAGE constants to the Language class.

Issue #1913618 by tim.plunkett, amateescu: Convert EntityFormControllerInterface to extend FormInterface.

Issue #1829224 by alexpott, pfrenssen, vijaycs85, lirantal: Convert the 'theme_default()' variable to CMI.

Issue #1919934 by larowlan: Change key of custom block vertical tabs to use 'advanced' instead of 'additional_settings()'.