As described in this post I found a workaround to not show the "State/Province/Region:" as output in order-status-page nor in the emails:
I simply translated the string with WPML by adding a blank-space as translation.
The result is that the State/... does not show on non-English sites, wher it is not appropriate.
This worked for the first part "State/Province/Region:", which is a translatable string.
The second part unfortunatedly is not.
Where can I find it to make it translatable e.g.: _e('CLICK TO SELECT')