diff --git a/src/wp-admin/network/site-new.php b/src/wp-admin/network/site-new.php
index 7882d0e378..4dd36392d4 100644
--- a/src/wp-admin/network/site-new.php
+++ b/src/wp-admin/network/site-new.php
@@ -65,10 +65,14 @@ if ( isset($_REQUEST['action']) && 'add-site' == $_REQUEST['action'] ) {
 	);
 
 	// Handle translation install for the new site.
-	if ( ! empty( $_POST['WPLANG'] ) && wp_can_install_language_pack() ) {
-		$language = wp_download_language_pack( wp_unslash( $_POST['WPLANG'] ) );
-		if ( $language ) {
-			$meta['WPLANG'] = $language;
+	if ( isset( $_POST['WPLANG'] ) ) {
+		if ( '' === $_POST['WPLANG'] ) {
+			$meta['WPLANG'] = ''; // en_US
+		} elseif ( wp_can_install_language_pack() ) {
+			$language = wp_download_language_pack( wp_unslash( $_POST['WPLANG'] ) );
+			if ( $language ) {
+				$meta['WPLANG'] = $language;
+			}
 		}
 	}
 
diff --git a/src/wp-includes/ms-functions.php b/src/wp-includes/ms-functions.php
index 113f37f284..ca8176124f 100644
--- a/src/wp-includes/ms-functions.php
+++ b/src/wp-includes/ms-functions.php
@@ -1092,7 +1092,10 @@ function wpmu_create_user( $user_name, $password, $email ) {
  * @return int|WP_Error Returns WP_Error object on failure, int $blog_id on success
  */
 function wpmu_create_blog( $domain, $path, $title, $user_id, $meta = array(), $site_id = 1 ) {
-	$defaults = array( 'public' => 0 );
+	$defaults = array(
+		'public' => 0,
+		'WPLANG' => get_site_option( 'WPLANG' ),
+	);
 	$meta = wp_parse_args( $meta, $defaults );
 
 	$domain = preg_replace( '/\s+/', '', sanitize_user( $domain, true ) );
@@ -1130,7 +1133,6 @@ function wpmu_create_blog( $domain, $path, $title, $user_id, $meta = array(), $s
 			update_option( $key, $value );
 	}
 
-	add_option( 'WPLANG', get_site_option( 'WPLANG' ) );
 	update_option( 'blog_public', (int) $meta['public'] );
 
 	if ( ! is_super_admin( $user_id ) && ! get_user_meta( $user_id, 'primary_blog', true ) )
diff --git a/tests/phpunit/tests/multisite/site.php b/tests/phpunit/tests/multisite/site.php
index e944197f7b..f6215e940e 100644
--- a/tests/phpunit/tests/multisite/site.php
+++ b/tests/phpunit/tests/multisite/site.php
@@ -926,6 +926,52 @@ class Tests_Multisite_Site extends WP_UnitTestCase {
 		);
 	}
 
+	/**
+	 * @ticket 36918
+	 */
+	function test_new_blog_locale() {
+		$current_site = get_current_site();
+
+		add_filter( 'sanitize_option_WPLANG', array( $this, 'filter_allow_unavailable_languages' ), 10, 3 );
+		update_site_option( 'WPLANG', 'de_DE' );
+		remove_filter( 'sanitize_option_WPLANG', array( $this, 'filter_allow_unavailable_languages' ), 10 );
+
+		// No locale, use default locale.
+		add_filter( 'sanitize_option_WPLANG', array( $this, 'filter_allow_unavailable_languages' ), 10, 3 );
+		$blog_id = wpmu_create_blog( $current_site->domain, '/de-de/', 'New Blog', get_current_user_id() );
+		remove_filter( 'sanitize_option_WPLANG', array( $this, 'filter_allow_unavailable_languages' ), 10 );
+
+		$this->assertNotWPError( $blog_id );
+		$this->assertSame( 'de_DE', get_blog_option( $blog_id, 'WPLANG' ) );
+
+		// Custom locale.
+		add_filter( 'sanitize_option_WPLANG', array( $this, 'filter_allow_unavailable_languages' ), 10, 3 );
+		$blog_id = wpmu_create_blog( $current_site->domain, '/es-es/', 'New Blog', get_current_user_id(), array( 'WPLANG' => 'es_ES' ) );
+		remove_filter( 'sanitize_option_WPLANG', array( $this, 'filter_allow_unavailable_languages' ), 10 );
+
+		$this->assertNotWPError( $blog_id );
+		$this->assertSame( 'es_ES', get_blog_option( $blog_id, 'WPLANG' ) );
+
+		// en_US locale.
+		add_filter( 'sanitize_option_WPLANG', array( $this, 'filter_allow_unavailable_languages' ), 10, 3 );
+		$blog_id = wpmu_create_blog( $current_site->domain, '/en-us/', 'New Blog', get_current_user_id(), array( 'WPLANG' => '' ) );
+		remove_filter( 'sanitize_option_WPLANG', array( $this, 'filter_allow_unavailable_languages' ), 10 );
+
+		$this->assertNotWPError( $blog_id );
+		$this->assertSame( '', get_blog_option( $blog_id, 'WPLANG' ) );
+	}
+
+	/**
+	 * Allows to set the WPLANG option to any language.
+	 *
+	 * @param string $value          The sanitized option value.
+	 * @param string $option         The option name.
+	 * @param string $original_value The original value passed to the function.
+	 * @return string The orginal value.
+	 */
+	function filter_allow_unavailable_languages( $value, $option, $original_value ) {
+		return $original_value;
+	}
 }
 
 endif;