Always a good thought, but I've already tried this ( as well as launching Calc under the root user ) without noticing any changes in symptoms. I'm suspecting a dependent file has gotten corrupted ( or deleted ) during one of the SW updates, as the loss of this functionality in Calc seems to be capricious as to when it hits most affected users.
It doesn't seem to be associated with any specific update, and it has been occurring since at least 12.6.4 or before for some of the users I've had contact with ( and from anecdotal reports I've found so far ). It just hits when it hits, and the symptoms are identical for all of the affected users I've found, so far.
Every time I choose the 'Currency' choice from Calc's drop-down menu ( the only way to access it now ) there is a brief spike in processor usage from the app, but I haven't found any new traffic going out over the network ports while actively scanning them during that app change ( as the app would presumably be making a network connection to ascertain the latest currency exchange rates, either at launch, or upon selecting 'Currency' as the desired conversion ).
If anyone finds some additional clues to solving this one, please let us all know. :- )