btoa takes bytes not unicde string, encode utf8 data first

static/js/exportAnnotationsDialog.js

@@ -124,11 +124,11 @@ pandora.ui.exportAnnotationsDialog = function(options) {
         $link.attr({
             download: options.title + ' - '
                 + Ox.getObjectById(layers, layer).title + '.' + format,
-            href: 'data:text/plain;base64,' + btoa(
+            href: 'data:text/plain;base64,' + btoa(Ox.encodeUTF8(
                 format == 'json'
                 ? JSON.stringify(items, null, '    ')
                 : Ox.formatSRT(items)
-            )
+            ))
         });
     }