Issue #2500525 by dawehner, catch, pjonckiere, mpdonadio, Wim Leers, jhodgdon: Time ago/hence date/time formatting breaks caching; needs appropriate max age or javascript

Issue #2568613 by alexpott, lauriii, pwolanin: Remove HTML support from date formats and replace remaining !placeholder where format_date() and 'date.formatter' => format() are used

Issue #2502571 by pjonckiere, mpdonadio, catch, jhodgdon: Date format granularity should only render adjacent units

Issue #2456521 by pjonckiere, mpdonadio, jhodgdon, rteijeiro, David_Rothstein, xjm: Add DateFormatter::formatDiff() as a non-buggy alternative to DateFormatter::formatInterval() when the start and end of the interval are known

Issue #2429443 by vijaycs85, rteijeiro, penyaskito, gloob, xjm, nod_, geertvd, pjonckiere, alexpott, Wim Leers, Gábor Hojtsy, Fabianx, tim.plunkett: Date format form is unusable

Revert "Issue #2429443 by vijaycs85, rteijeiro, penyaskito, gloob, xjm, nod_, geertvd, Wim Leers, Gábor Hojtsy, Fabianx, pjonckiere, tim.plunkett: Date format form is unusable"

This reverts commit 37e278b4.

Issue #2429443 by vijaycs85, rteijeiro, penyaskito, gloob, xjm, nod_, geertvd, Wim Leers, Gábor Hojtsy, Fabianx, pjonckiere, tim.plunkett: Date format form is unusable

Revert "Issue #2457345 by vijaycs85: Remove unnecessary format lookup in \Drupal\Core\Datetime\DateFormatter::dateFormat for 'custom' format"

This reverts commit 744514b9.

Issue #2457345 by vijaycs85: Remove unnecessary format lookup in \Drupal\Core\Datetime\DateFormatter::dateFormat for 'custom' format

Issue #2340667 by YesCT, Pedro Lozano, alexpott, martin107: Protect Drupal\Core\Language\Language::id, and use getId().

Issue #2216541 by jhodgdon, Gábor Hojtsy: Fill in topic/@defgroup docs for Internationalization overview.

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

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

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

Issue #2111349 by dawehner, tim.plunkett: Move format_plural to the string translation service and format_interval to the date service.

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

Issue #2098089 by penyaskito, Schnitzel, tim.plunkett, YesCT, EllaTheHarpy, Gábor Hojtsy: Fixed Date formats cannot be translated (the core UIs are useless).

Issue #1957142 follow-up by dawehner, jibran: Fix a few more config() => Drupal::config() stragglers.

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