Issue #2257283 by cs_shadow, filijonka: Fix obsolete references to form_set_error() in FormErrorInterface docs

Issue #2254495 by ParisLiakos, alexpott: Move language_admin_predefined_list to ConfigurableLanguageManager.

Issue #2250335 by drupaledmonk, pingwin4eg | jhodgdon: Forum hook_help still using URL instead of route.

Issue #1919916 by oadaeh, larowlan, jessehs, babruix: Change label of custom block default body field from "Block body" to just "Body".

Issue #2240463 by robertdbailey, balagan, holly.ross.drupal: Fix text: languages are not "enabled/disabled" anymore, they are added/removed.

Issue #2240007 by sun, YesCT, mr.baileys | Gábor Hojtsy: Regression: early installer is not in RTL after selecting RTL language.

Issue #1939008 by sun, joelpittet, gnuget, Gokul N K, sphism, drupalninja99, c4rl, Cottser, mdrummond, long wave, steveoliver, andypost, Fabianx | jenlampton: Convert theme_table() to Twig.

Issue #2099131 by jessebeach, Wim Leers, catch, Berdir, benjifisher, martin107, andypost: Use #pre_render pattern for entity render caching.

Issue #2079797 by ParisLiakos, Xano, amateescu, tim.plunkett: Provide a trait for $this->t() and $this->formatPlural().

Issue #2158571 by tstoeckler, dawehner, kgoel, tim.plunkett, catch, effulgentsia: Routes added in RouteSubscribers cannot be altered.