To create country-specific fields for the Legal Entity object in SAP SuccessFactors Employee Central, you should define these fields as an HRIS element within the Country-Specific Field section of the Corporate Data Model. This approach allows the system to manage country-specific attributes effectively. The 'Valid When' association is utilized to ensure that these fields are applicable only when certain conditions, such as the country of registration, are met. This configuration ensures that the Legal Entity object contains fields relevant to specific countries, facilitating accurate data management and compliance with local regulations.