address issue 5289 - set false locale

Author: archmoj

src/plots/plots.js

@@ -667,7 +667,7 @@ function emptySubplotLists() {
  */
 function getFormatObj(gd, formatKeys) {
     var locale = gd._context.locale;
-    if(!locale) locale === 'en-US';
+    if(!locale) locale = 'en-US';
 
     var formatDone = false;
     var formatObj = {};