diff -u b/core/lib/Drupal/Core/Language/Language.php b/core/lib/Drupal/Core/Language/Language.php
--- b/core/lib/Drupal/Core/Language/Language.php
+++ b/core/lib/Drupal/Core/Language/Language.php
@@ -134,14 +134,14 @@
   /**
    * {@inheritdoc}
    */
-  public function getLangCode() {
+  public function getLangcode() {
     return $this->id;
   }
 
   /**
    * {@inheritdoc}
    */
-  public function setLangCode($langcode) {
+  public function setLangcode($langcode) {
     $this->id = $langcode;
 
     return $this;
diff -u b/core/lib/Drupal/Core/Language/LanguageInterface.php b/core/lib/Drupal/Core/Language/LanguageInterface.php
--- b/core/lib/Drupal/Core/Language/LanguageInterface.php
+++ b/core/lib/Drupal/Core/Language/LanguageInterface.php
@@ -115,7 +115,7 @@
    *
    * @return string
    */
-  public function getLangCode();
+  public function getLangcode();
 
   /**
    * Sets the language code.
@@ -124,7 +124,7 @@
    *
    * @return $this
    */
-  public function setLangCode($langcode);
+  public function setLangcode($langcode);
 
   /**
    * Gets the text direction (left-to-right or right-to-left).
diff -u b/core/tests/Drupal/Tests/Core/Language/LanguageUnitTest.php b/core/tests/Drupal/Tests/Core/Language/LanguageUnitTest.php
--- b/core/tests/Drupal/Tests/Core/Language/LanguageUnitTest.php
+++ b/core/tests/Drupal/Tests/Core/Language/LanguageUnitTest.php
@@ -52,13 +52,13 @@
   }
 
   /**
-   * @covers \Drupal\Core\Language\Language::getLangCode()
-   * @covers \Drupal\Core\Language\Language::setLangCode()
+   * @covers \Drupal\Core\Language\Language::getLangcode()
+   * @covers \Drupal\Core\Language\Language::setLangcode()
    */
-  public function testGetLangCode() {
+  public function testGetLangcode() {
     $language_code = $this->randomName(2);
-    $this->assertSame(spl_object_hash($this->language), spl_object_hash($this->language->setLangCode($language_code)));
-    $this->assertSame($language_code, $this->language->getLangCode());
+    $this->assertSame(spl_object_hash($this->language), spl_object_hash($this->language->setLangcode($language_code)));
+    $this->assertSame($language_code, $this->language->getLangcode());
   }
 
   /**