Index: src/wp-admin/includes/ms.php
===================================================================
--- src/wp-admin/includes/ms.php	(revision 28905)
+++ src/wp-admin/includes/ms.php	(working copy)
@@ -557,18 +557,18 @@
 // See "import_allow_fetch_attachments" and "import_attachment_size_limit" filters too.
 
 function mu_dropdown_languages( $lang_files = array(), $current = '' ) {
-	$flag = false;
+	$en_us = $en_gb = false;
 	$output = array();
 
 	foreach ( (array) $lang_files as $val ) {
 		$code_lang = basename( $val, '.mo' );
 
 		if ( $code_lang == 'en_US' ) { // American English
-			$flag = true;
+			$en_us = true;
 			$ae = __( 'American English' );
 			$output[$ae] = '<option value="' . esc_attr( $code_lang ) . '"' . selected( $current, $code_lang, false ) . '> ' . $ae . '</option>';
 		} elseif ( $code_lang == 'en_GB' ) { // British English
-			$flag = true;
+			$en_gb = true;
 			$be = __( 'British English' );
 			$output[$be] = '<option value="' . esc_attr( $code_lang ) . '"' . selected( $current, $code_lang, false ) . '> ' . $be . '</option>';
 		} else {
@@ -578,8 +578,13 @@
 
 	}
 
-	if ( $flag === false ) // WordPress english
+	if ( ! $en_us && ! $en_gb ) {
+		// No English languages installed, display the default language as English
 		$output[] = '<option value=""' . selected( $current, '', false ) . '>' . __( 'English' ) . "</option>";
+	} else if ( ! $en_us && $en_gb ) {
+		// British English is installed, display the default language as American English
+		$output[] = '<option value=""' . selected( $current, '', false ) . '>' . __( 'American English' ) . "</option>";
+	}
 
 	// Order by name
 	uksort( $output, 'strnatcasecmp' );