Merge pull request #2560 from edx/sarina/fix-i18n-xmodule-sequence

i18n Sequence XModule

common/lib/xmodule/xmodule/js/src/sequence/display.coffee

@@ -144,7 +144,7 @@ class @Sequence
       @render new_position
     else
       alert_template = gettext("Sequence error! Cannot navigate to tab %(tab_name)s in the current SequenceModule. Please contact the course staff.")
-      alert_text = interpolate(alert_text, {tab_name: new_position}, true)
+      alert_text = interpolate(alert_template, {tab_name: new_position}, true)
       alert alert_text
 
   next: (event) => @_change_sequential 'seq_next', event