I run the NAV Server Tier under my own account, so regional settings are itlalian; It seems the service tier does not take the regional settings of the user who runs the service
Solution --> Use User Personalization table
>> Make an entry in Table User Personalization (2000000073) for the user that runs the NAV Server.
>> Set there the language to the desired language. The EVALUATE is then working fine too with the proper date format.
So, it is not considering the Regional Settings.