Index: src/wp-includes/class-wp-editor.php
===================================================================
--- src/wp-includes/class-wp-editor.php	(revision 29713)
+++ src/wp-includes/class-wp-editor.php	(working copy)
@@ -600,6 +600,8 @@
 				}
 			}
 
+			$body_class .= ' locale-' . sanitize_html_class( strtolower( str_replace( '_', '-', get_locale() ) ) );
+
 			if ( !empty($set['tinymce']['body_class']) ) {
 				$body_class .= ' ' . $set['tinymce']['body_class'];
 				unset($set['tinymce']['body_class']);
Index: src/wp-includes/css/editor.css
===================================================================
--- src/wp-includes/css/editor.css	(revision 29713)
+++ src/wp-includes/css/editor.css	(working copy)
@@ -807,6 +807,14 @@
 	box-sizing: border-box;
 }
 
+.rtl .wp-editor-area {
+	font-family: Tahoma, Monaco, monospace;
+}
+
+.locale-he-il .wp-editor-area {
+	font-family: Arial, Monaco, monospace;
+}
+
 .wp-editor-container textarea.wp-editor-area {
 	width: 100%;
 	margin: 0;
Index: src/wp-includes/js/tinymce/skins/wordpress/wp-content.css
===================================================================
--- src/wp-includes/js/tinymce/skins/wordpress/wp-content.css	(revision 29713)
+++ src/wp-includes/js/tinymce/skins/wordpress/wp-content.css	(working copy)
@@ -17,6 +17,14 @@
 	margin: 9px 10px;
 }
 
+body.rtl {
+	font-family: Tahoma, "Times New Roman", "Bitstream Charter", Times, serif;
+}
+
+body.locale-he-il {
+	font-family: Arial, "Times New Roman", "Bitstream Charter", Times, serif;
+}
+
 body.wp-autoresize {
 	max-width: 100%;
 	overflow: visible !important;