diff --git a/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php b/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
index 97592d2..ef87eb6 100644
--- a/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
@@ -34,10 +34,12 @@ function testLanguageConfiguration() {
 
     // Check if the Default English language has no path prefix.
     $this->drupalGet('admin/config/regional/language/detection/url');
-    $this->assertFieldByXPath('//input[@name="prefix[en]"]', '', 'Default English has no path prefix.');
+    // Default English has no path prefix.
+    $this->assertSession()->fieldExists('prefix[en]');
 
     // Check that Add language is a primary button.
     $this->drupalGet('admin/config/regional/language/add');
+    // Add language is a primary button.
     $this->assertFieldByXPath('//input[contains(@class, "button--primary")]', 'Add language', 'Add language is a primary button');
 
     // Add predefined language.
diff --git a/core/modules/language/tests/src/Functional/LanguageListTest.php b/core/modules/language/tests/src/Functional/LanguageListTest.php
index bdbda9e..ecad682 100644
--- a/core/modules/language/tests/src/Functional/LanguageListTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageListTest.php
@@ -39,7 +39,8 @@ function testLanguageList() {
       'predefined_langcode' => 'fr',
     );
     $this->drupalPostForm('admin/config/regional/language/add', $edit, t('Add language'));
-    $this->assertText('French', 'Language added successfully.');
+    // Language added successfully.
+    $this->assertText('French');
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE]));
 
     // Get the weight of the last language and check that the weight is one unit
@@ -61,8 +62,10 @@ function testLanguageList() {
     );
     $this->drupalPostForm('admin/config/regional/language/add', $edit, t('Add custom language'));
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE]));
-    $this->assertRaw('"edit-languages-' . $langcode . '-weight"', 'Language code found.');
-    $this->assertText(t($name), 'Test language added.');
+    // Language code found.
+    $this->assertRaw('"edit-languages-' . $langcode . '-weight"');
+    // Test language added.
+    $this->assertText(t($name));
 
     $language = \Drupal::service('language_manager')->getLanguage($langcode);
     $english = \Drupal::service('language_manager')->getLanguage('en');
@@ -70,31 +73,36 @@ function testLanguageList() {
     // Check if we can change the default language.
     $path = 'admin/config/regional/language';
     $this->drupalGet($path);
-    $this->assertFieldChecked('edit-site-default-language-en', 'English is the default language.');
+    // English is the default language.
+    $this->assertFieldChecked('edit-site-default-language-en');
     // Change the default language.
     $edit = array(
       'site_default_language' => $langcode,
     );
     $this->drupalPostForm(NULL, $edit, t('Save configuration'));
     $this->rebuildContainer();
-    $this->assertNoFieldChecked('edit-site-default-language-en', 'Default language updated.');
+    // Default language updated.
+    $this->assertNoFieldChecked('edit-site-default-language-en');
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE, 'language' => $language]));
 
     // Ensure we can't delete the default language.
     $this->drupalGet('admin/config/regional/language/delete/' . $langcode);
-    $this->assertResponse(403, 'Failed to delete the default language.');
+    // Failed to delete the default language.
+    $this->assertResponse(403);
 
     // Ensure 'Edit' link works.
     $this->drupalGet('admin/config/regional/language');
     $this->clickLink(t('Edit'));
-    $this->assertTitle(t('Edit language | Drupal'), 'Page title is "Edit language".');
+    // Page title is "Edit language".
+    $this->assertTitle(t('Edit language | Drupal'));
     // Edit a language.
     $name = $this->randomMachineName(16);
     $edit = array(
       'label' => $name,
     );
     $this->drupalPostForm('admin/config/regional/language/edit/' . $langcode, $edit, t('Save language'));
-    $this->assertRaw($name, 'The language has been updated.');
+    // The language has been updated.
+    $this->assertRaw($name);
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE, 'language' => $language]));
 
     // Change back the default language.
@@ -106,23 +114,27 @@ function testLanguageList() {
     // Ensure 'delete' link works.
     $this->drupalGet('admin/config/regional/language');
     $this->clickLink(t('Delete'));
-    $this->assertText(t('Are you sure you want to delete the language'), '"Delete" link is correct.');
+    // "Delete" link is correct.
+    $this->assertText(t('Are you sure you want to delete the language'));
     // Delete a language.
     $this->drupalGet('admin/config/regional/language/delete/' . $langcode);
     // First test the 'cancel' link.
     $this->clickLink(t('Cancel'));
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE, 'language' => $english]));
-    $this->assertRaw($name, 'The language was not deleted.');
+    // The language was not deleted.
+    $this->assertRaw($name);
     // Delete the language for real. This a confirm form, we do not need any
     // fields changed.
     $this->drupalPostForm('admin/config/regional/language/delete/' . $langcode, array(), t('Delete'));
     // We need raw here because %language and %langcode will add HTML.
     $t_args = array('%language' => $name, '%langcode' => $langcode);
-    $this->assertRaw(t('The %language (%langcode) language has been removed.', $t_args), 'The test language has been removed.');
+    // The test language has been removed.
+    $this->assertRaw(t('The %language (%langcode) language has been removed.', $t_args));
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE, 'language' => $english]));
     // Verify that language is no longer found.
     $this->drupalGet('admin/config/regional/language/delete/' . $langcode);
-    $this->assertResponse(404, 'Language no longer found.');
+    // Language no longer found.
+    $this->assertResponse(404);
 
     // Delete French.
     $this->drupalPostForm('admin/config/regional/language/delete/fr', array(), t('Delete'));
@@ -130,11 +142,13 @@ function testLanguageList() {
     $this->rebuildContainer();
     // We need raw here because %language and %langcode will add HTML.
     $t_args = array('%language' => 'French', '%langcode' => 'fr');
-    $this->assertRaw(t('The %language (%langcode) language has been removed.', $t_args), 'The French language has been removed.');
+    // The French language has been removed.
+    $this->assertRaw(t('The %language (%langcode) language has been removed.', $t_args));
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE]));
     // Verify that language is no longer found.
     $this->drupalGet('admin/config/regional/language/delete/fr');
-    $this->assertResponse(404, 'Language no longer found.');
+    // Language no longer found.
+    $this->assertResponse(404);
     // Make sure the "language_count" state has not changed.
 
     // Ensure we can delete the English language. Right now English is the only
@@ -150,37 +164,42 @@ function testLanguageList() {
     );
     $this->drupalPostForm('admin/config/regional/language/add', $edit, t('Add custom language'));
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE]));
-    $this->assertText($name, 'Name found.');
+    $this->assertText($name);
 
     // Check if we can change the default language.
     $path = 'admin/config/regional/language';
     $this->drupalGet($path);
-    $this->assertFieldChecked('edit-site-default-language-en', 'English is the default language.');
+    // English is the default language.
+    $this->assertFieldChecked('edit-site-default-language-en');
     // Change the default language.
     $edit = array(
       'site_default_language' => $langcode,
     );
     $this->drupalPostForm(NULL, $edit, t('Save configuration'));
     $this->rebuildContainer();
-    $this->assertNoFieldChecked('edit-site-default-language-en', 'Default language updated.');
+    // Default language updated.
+    $this->assertNoFieldChecked('edit-site-default-language-en');
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE, 'language' => $language]));
 
     $this->drupalPostForm('admin/config/regional/language/delete/en', array(), t('Delete'));
     // We need raw here because %language and %langcode will add HTML.
     $t_args = array('%language' => 'English', '%langcode' => 'en');
-    $this->assertRaw(t('The %language (%langcode) language has been removed.', $t_args), 'The English language has been removed.');
+    // The English language has been removed.
+    $this->assertRaw(t('The %language (%langcode) language has been removed.', $t_args));
     $this->rebuildContainer();
 
     // Ensure we can't delete a locked language.
     $this->drupalGet('admin/config/regional/language/delete/und');
-    $this->assertResponse(403, 'Can not delete locked language');
+    // Can not delete locked language
+    $this->assertResponse(403);
 
     // Ensure that NL cannot be set default when it's not available.
     $this->drupalGet('admin/config/regional/language');
     $extra_values = '&site_default_language=nl';
     $this->drupalPostForm(NULL, array(), t('Save configuration'), array(), array(), NULL, $extra_values);
     $this->assertText(t('Selected default language no longer exists.'));
-    $this->assertNoFieldChecked('edit-site-default-language-xx', 'The previous default language got deselected.');
+    // The previous default language got deselected.
+    $this->assertNoFieldChecked('edit-site-default-language-xx');
   }
 
   /**
diff --git a/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php b/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
index 4c274e5..9e81989 100644
--- a/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
@@ -105,7 +105,8 @@ function testInfoAlterations() {
     $this->assertFalse(isset($negotiation[$interface_method_id]), 'Interface language negotiation method removed from the stored settings.');
 
     $this->drupalGet('admin/config/regional/language/detection');
-    $this->assertNoFieldByName($form_field, NULL, 'Interface language negotiation method unavailable.');
+    // Interface language negotiation method unavailable..
+    $this->assertNoFieldByName($form_field, NULL);
 
     // Check that type-specific language negotiation methods can be assigned
     // only to the corresponding language types.
diff --git a/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
index 1b43863..a4c78fa 100644
--- a/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
+++ b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
@@ -129,6 +129,27 @@ protected function assertFieldByName($name, $value = NULL) {
   }
 
   /**
+   * Asserts that a field exists with the given name and value.
+   *
+   * @param string $name
+   *   Name of field to assert.
+   * @param string $value
+   *   (optional) Value of the field to assert. You may pass in NULL (default)
+   *   to skip checking the actual value, while still checking that the field
+   *   exists.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->fieldNotExists() or
+   *   $this->assertSession()->fieldValueNotEquals() instead.
+   */
+  protected function assertNoFieldByName($name, $value = NULL) {
+    $this->assertSession()->fieldNotExists($name);
+    if ($value !== NULL) {
+      $this->assertSession()->fieldValueNotEquals($name, (string) $value);
+    }
+  }
+
+  /**
    * Asserts that a field exists with the given ID and value.
    *
    * @param string $id