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

Issue #1751348 by heyrocker, vijaycs85, julien, Gábor Hojtsy: Convert locale settings to configuration system.

Issue #1832614 by Schnitzel, smiletrl, -enzo-: Fixed Unchanged strings on page become customized when editing others.

Issue #1789750 by droplet: Fixed Fatal error: Call to undefined function language_negotiation_url_prefixes_update().

Issue #1785086 by Jose Reyero, Gábor Hojtsy, catch, loganfsmyth, nedjo, stella: Added Introduce a generic API for interface translation strings.

Issue #1711070 by kid_icarus, tim.plunkett, xjm, droplet, zendoodles and cam8001: Convert tests to use ::$modules property instead of parent::setUp($modules).

Issue #1452188 by Schnitzel, droplet, Sutharsan, Bojhan, Kristen Pol, Gábor Hojtsy, ershov.andrey, perusio, nod_, rvilar, andypost: Added New UI for string translation.

- Patch #730060 by beejeebus, catch, Damien Tournoud, moshe weitzman, msonnabaum, oriol_e9g, aspilicious: Fixed Replace CACHE_TEMPORARY, cache_clear_all() (no arguments) and minimum cache lifetime with cache tags support.