NodeTranslationUITest should use API to set up language

    $edit = ['field_storage[subform][cardinality_number]' => 2];
    $this->drupalGet('admin/structure/types/manage/article/fields/node.article.field_image');
    $this->submitForm($edit, 'Save');

    // Make the image field non-translatable.
    $edit = ['settings[node][article][fields][field_image]' => FALSE];
    $this->drupalGet('admin/config/regional/content-language');
    $this->submitForm($edit, 'Save configuration');

    $edit['use_admin_theme'] = FALSE;
    $this->drupalGet('admin/appearance');
    $this->submitForm($edit, 'Save configuration');

Could these be converted too?

LGTM

+++ b/core/modules/node/tests/src/Functional/NodeTranslationUITest.php
@@ -258,21 +263,19 @@ public function testTranslationLinkTheme() {
+    $this->container->get('router.builder')->rebuild();

Why do we need to do a router rebuild here but not in the earlier case? This sort of thing makes me take pause about these conversions because it's not clear why we have to do this now when we didn't before.

The Needs Review Queue Bot → tested this issue.

While you are making the above changes, we recommend that you convert this patch to a merge request → . Merge requests are preferred over patches. Be sure to hide the old patch files as well. (Converting an issue to a merge request without other contributions to the issue will not receive credit.)

> Why do we need to do a router rebuild here but not in the earlier case? This sort of thing makes me take pause about these conversions because it's not clear why we have to do this now when we didn't before.

Let's try without it :)
Part of the problem with these conversions is that the language system's API is complicated and not well-documented.