Issue #2780549 by andrewbelcher, alexpott, mpdonadio: FormattedDateDiff::$maxAge never applied to caches

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2600118 by aerozeppelin, anil280988, stefan.r, dawehner, andypost, sdstyles, ramirez.gerardo: Return TranslationWrapper in t() and $this->t() directly

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 #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

Issue #2212427 by Mixologic, YesCT, Sutharsan, mgriego, icseh., visabhishek, znerol: Use interface instead of class name for language manager where appropriate.

Issue #2149197 by penyaskito, mikey_p, vijaycs85, herom: Replace format_interval with \Drupal::service('date')->formatInterval().

Issue #697760 by sun: Replace getInfo() in tests with native phpDoc + annotations (following PHPUnit).

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.