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

Issue #2171071 by jessebeach, dawehner, chakrapani, longwave, Gábor Hojtsy, xjm, Wim Leers: Rename drupal_add_library() to _drupal_add_library() and remove its uses.

Somehow this broke PHPUnit, so rolling back for now.

This reverts commit 91b465bd.

Issue #2074037 by Wim Leers, effulgentsia: Add drupalPostUrl() — drupalPost()/drupalPostAjax() are for forms only, D8 JS performs non-form HTTP requests.

Issue #1797364 by dcam,  lazysoundsystem, Lars Toomre, neetu morwani, izus, boran, xjm: Remove t() from test asserts in locale module

Issue #2029505 by penyaskito, YesCT, Gábor Hojtsy: Fixed Exporting translations does not correctly generate empty strings.

Issue #1813762 by ParisLiakos, Jose Reyero, YesCT, japicoder, attiks: Introduce unified interfaces, use dependency injection for interface translation.

Issue #1658842 by penyaskito, attiks, webflo: Added Introduce a translations:// stream wrapper to access the .po file directory.

Issue #1737148 by nod_, SebCorbin, larowlan, tim.plunkett, Albert Volkman, nick_schuch, sun: Explicitly declare all JS dependencies, don't use drupal_add_js().

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