The Nationality field from the Contact TI (header section) is not available via OData.
Nationality > /CurrentCommon/Person/NationalityCountryCode
SAP Cloud for Customer
Our developers are planning to make this available with one of the future releases.
Please note that it is not possible for our Support Team to provide you additional information regarding the availability of this feature in a future release.
KBA , LOD-CRM-CON , Contact , Problem