Ticket #37819: 37819.diff

src/wp-includes/l10n.php

@@ -563 +563 @@
         $mo = new MO();
         if ( !$mo->import_from_file( $mofile ) ) return false;
 
-        if ( isset( $l10n[$domain] ) )
-                $mo->merge_with( $l10n[$domain] );
+        if ( isset( $l10n[$domain] ) ) {
 
+                $is_regular = false;
+                foreach ( array(
+                        WP_LANG_DIR . '/plugins',
+                        WP_LANG_DIR . '/themes',
+                ) as $path ) {
+                        $is_regular = strstr( $mofile, $path );
+
+                        if ( $is_regular ) {
+                                $is_regular = true;
+                                break;
+                        }
+                }
+
+                if ( ! $is_regular && 'default' !== $domain ) {
+                        $mo->merge_originals_with( $l10n[$domain] );
+                } else {
+                        $mo->merge_with( $l10n[$domain] );
+                }
+        }
+
         unset( $l10n_unloaded[ $domain ] );
 
         $l10n[$domain] = &$mo;