diff --git a/core/modules/language/src/Form/LanguageAddForm.php b/core/modules/language/src/Form/LanguageAddForm.php
index f0b1029..b33c907 100644
--- a/core/modules/language/src/Form/LanguageAddForm.php
+++ b/core/modules/language/src/Form/LanguageAddForm.php
@@ -54,6 +54,7 @@ public function form(array $form, FormStateInterface $form_state) {
       ),
       '#validate' => array('::validatePredefined'),
       '#submit' => array('::submitForm', '::save'),
+      '#button_type' => 'primary',
     );
 
     $custom_language_states_conditions = array(
diff --git a/core/modules/language/src/Tests/LanguageConfigurationTest.php b/core/modules/language/src/Tests/LanguageConfigurationTest.php
index fdaf217..025da77 100644
--- a/core/modules/language/src/Tests/LanguageConfigurationTest.php
+++ b/core/modules/language/src/Tests/LanguageConfigurationTest.php
@@ -41,11 +41,15 @@ function testLanguageConfiguration() {
     $this->drupalGet('admin/config/regional/language/detection/url');
     $this->assertFieldByXPath('//input[@name="prefix[en]"]', '', 'Default English has no path prefix.');
 
+    // Check that Add language is a primary button.
+    $this->drupalGet('admin/config/regional/language/add');
+    $this->assertFieldByXPath('//input[contains(@class, "button--primary")]', 'Add language', 'Add language is a primary button');
+
     // Add predefined language.
     $edit = array(
       'predefined_langcode' => 'fr',
     );
-    $this->drupalPostForm('admin/config/regional/language/add', $edit, 'Add language');
+    $this->drupalPostForm(NULL, $edit, 'Add language');
     $this->assertText('French');
     $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE]), [], 'Correct page redirection.');
     // Langcode for Languages is always 'en'.