Config entities upcast from the request always get default language context

Here is an untested test only. :D

1. +++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php
   @@ -144,6 +144,31 @@ function testConfigTranslation() {
   +    // Enable the contact module.
   +    $this->drupalPostForm('admin/modules', array('modules[Core][contact][enable]' => "1"), t('Save configuration'));
   +    $this->resetAll();
   

   Can't we simply make contact.module a requirement of the test?

2. +++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php
   @@ -144,6 +144,31 @@ function testConfigTranslation() {
   +    // translation. This test ensures the entity loaded from the request
   +    // upcasting will already work.
   

   I think "work" is not very precise. I would suggest "the entity loaded from the request upcasting has active locale overrides."

3. +++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php
   @@ -144,6 +144,31 @@ function testConfigTranslation() {
   +    $this->assertTest($categry_label);
   

   Typo

Marking needs work for 3. at least.

Just put both patches together. Looks good. Fixed two issues in the test from comment 3.

+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleConfigTranslationTest.php
@@ -144,6 +144,31 @@ function testConfigTranslation() {
+    $this->drupalGet($langcode . '/contact/feedback');
+    $this->assertTest($categry_label);

This page callbacks needs the permission "access site-wide contact form".

Typo in $categry_label

Ups.

Looks good to me. Let's get this in! Marking blocker for #1952394: Add configuration translation user interface module in core since this fails the perfect tests there :) The fails appeared now because contact was just recently converted to the routing system and upcast in the routing vs. the old menu hook based method.

Looks good, thanks. The bot can prove me wrong, if it wants, but for humans this is RTBC.

x-post.

Committed and pushed to 8.x. Thanks!

Woot, yay!