I have just created an import script to import my collection from a csv file into Numista - it is available here:
https://github.com/pwclay/NumistaImporter
The process it follows is:
1/ Match english country name with Numista country name (from the incomplete list in countries.csv)
2/ Look up catalog code & country & if only one match, carry on.
3/ Look up the year, mint & type. If there is a match for all 3, add it to the collection. If there is only one match for the year only, add it to the collection. Otherwise note the number of matches.
Further details & instructions are in the readme.
Each coin takes 3 API calls to be added, so you are limited to 666 coins added each month if all of the data is perfect.
In my last import run, I searched 728 types. These returned 686 matches to check the issues, and resulted in 578 coins being added to my collection. The coins that couldn't be matched by the script I added manually (150).
I hope that this saves people some time in bringing their collection to Numista. With small modifications it should be able to be used to import directly from the Numista export file.