How can I find out what key the user interface is using to look for a label?
There also may be labels shown in the UI which were translated on the server. For these, you should enable DEBUG for this class (via JMX):
As of CL 1071730 on 3.7, it produces logs like this:
05-02 15:20:36,464 DEBUG (0.0.0-80-exec-1) <10014,10108> [ ResourceMessageBundle] i18n: meta.enum.Undefined.State.Intransit
If you combine both the Chrome console output with these server side logs, you should get a sense of all labels.