It would be very cool if the Monzo widget (& the app), displayed the converted card balance & spent today in your local currency while you were abroad.
Failing that, since your use case is a bit of an edge case, a developer might need to get this set up. I’d hope that by the time the Monzo API is ready, MasterCard will have made their conversion rate available via their APIs which would make it straightforward to build an widget using Zapier / Workflow.