Issue #1803638 by vijaycs85, YesCT: Improve default language change process (ui and help text).

...odules/block/lib/Drupal/block/Tests/BlockLanguageTest.php

core/modules/language/language.admin.inc

core/modules/language/language.module

...e/lib/Drupal/language/Tests/LanguageConfigurationTest.php

...s/language/lib/Drupal/language/Tests/LanguageListTest.php

...lib/Drupal/language/Tests/LanguagePathMonolingualTest.php

...ules/locale/lib/Drupal/locale/Tests/LocaleContentTest.php

.../locale/lib/Drupal/locale/Tests/LocaleTranslationTest.php

core/modules/locale/locale.module

...ode/lib/Drupal/node/Tests/NodeTypeInitialLanguageTest.php

...les/search/lib/Drupal/search/Tests/SearchLanguageTest.php