This is happening 100% reproducibly on the OU test server, with latest moodle.org master branch, but it is not happening for me on qa.moodle.net.

1. Log in as admin (or other role).
2. Go to the permissions page for any context (admin/roles/permissions.php?contextid=N).
3. Click the X icon by any role. (That is a dustbin icon in boost)

Expected result: pop-up opens with a confirmation message.

Actual result: pop-up opens saying [[confirmroleundefined,core_role]], and then the UI does not work.

If, at this point, you close the dialogue (e.g. press Esc) and then click the un-assign role X again, it works the second time. If you reload the page (F5) then it breaks again, for the first time you click an icon after that.