I have had similar issues before...

Last week, before upgrading to Mac OS Sierra - I changed my OS language away from Danish to english.
This I started getting problems with CWS. It simply won't start.

I get the error message "locale 'en_DK' cannot be set."

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I have now upgraded to Mac OS sierra ... and problem is the same. I have reinstalled CWS.
I have changed the system language back and forth between english and Danish. Same problem.
When clicking ok ... on the locale 'en_DK' cannot be set. the application hangs.

Any Ideas?