The language field is used when Sending Emails and SMS through RACE RESULT 12, to determine which lnaguage version of the template should be sent, if a multi-lingual template is used. 

The Language field is automatically filled when a participant registers using the Online Registration with the language used in the form at the time of registration. The field can also be filled when importing participants or edited using data manipulation. 

The default language field will take higher priority than any additional fields added with the same name (including translated versions).