Issue #2281905 by Berdir: Stop caching plugin discovery/info hooks by language.
Issue #2152215 by joelpittet, mr.baileys, benjifisher, martin107, rteijeiro, hussainweb, shanethehat, jenlampton, kpa, AnythonyR, EVIIILJ, kgoel, Cottser, dsdeiz, hanpersand, bayousoft: Convert theme_form_element_label() to Twig
Issue #2264753 by cfox612, Cottser, a-fro, joelpittet: Convert theme_update_last_check to update-last-check.html.twig.
Issue #2089331 by grom358 | thedavidmeister: [meta] Replace calls to check_plain() with Drupal\Component\Utility\String::checkPlain().
Issue #2080343 by connork, izus, rahul.shinde, lokapujya | mrsinguyen: Remove Unused local variables from system module.
Issue #2052473 by ricky.middaugh, lokapujya, Jalandhar, mgifford, jessebeach, BarisW, falcon03: Add aria-label or aria-describedby attributes to all <nav> elements.
Issue #2250325 by jhodgdon, azinck, splatio: Fixed Route book.render (path /book) does not seem to work.
Issue #1898420 by mondrake, joelpittet, InternetDevels, claudiu.cristea, c4rl, DamienMcKenna, Albert Volkman, shanethehat, thedavidmeister: Image.module - Convert theme_ functions to Twig.
Issue #2151821 by joelpittet, JacobSanford, jjcarrion, rteijeiro, c4rl, IshaDakota, pplantinga, gnuget, longwave, jeanfei, sbudker1: Convert theme_system_config_form() to Twig
Issue #2216549 by jhodgdon, steveoliver: Fill in @defgroup/topic docs for Render overview.
Issue #1898070 by benjifisher, jjcarrion, LinL, idflood, joelpittet, oshelach, tlattimore, Les Lim, sergey.semashko, jesse.d, bdgreen, jenlampton, Cottser, duellj, artofeclipse, vlad.dancer, steveoliver, EVIIILJ, c4rl, elv, OpenChimp: File.module - Convert theme_ functions to Twig.
Issue #1939092 by mgifford, dbazuin, jenlampton, azinoman, pwieck, Cottser, joelpittet, larowlan: Convert theme_mark() to Twig.
Issue #2228763 by larowlan, alexpott, martin107, jessebeach, xjm: Create a comment-type config entity and use that as comment bundles, require selection in field settings form.
Issue #2277481 by znerol: Remove persist flag from container.namespaces service.
Issue #1912610 by amitgoyal, BryanCGreen24, lokapujya, Rajendar Reddy, echoz, barraponto, LewisNyman, pixelwhip: Rename layout classes to follow the layout style naming convention.