Lang=”auto”

Hi,
When I first load the home page then lang attribute in html tag is set to “el” which is the default languge (lang=”el”).
If I switch to English it sets lang=”en” and it’s ok.
If now I switch back to Greek Language it sets to lang=”auto” and not lang=”el”. This fires an error with Wave (WCAG) rules that requires to be a valid language value.
I will appreciate your advice to solve this. Thank you.