When processing VAT returns Sage should use the country code of the Company for which you are doing the VAT return for and not use local window regional settings.

Currenlty you have leave Sage and go to your windows setting and change regional settings on the local PC being used to do the VAT return. This is ridiculous as user local windows setting should have no bearing on how sage calulates the VAT return. The company in sage is configured to ensure that Sage knows which country a company is trading in and therefore is the only source which should be used for determining the country for VAT returns. 

The current approach of using a local user windows settings, is both error prone and requiires the user to have privileges on their local PC to change these setting which also impact all windows functions, the user must also remember to switch them every time they are working on another company in sage. The current appoarch also provides a head ache for corporate IT as they have to allow users to be able to make changes to their profiles in Active directory.