error in PHP conditional

You’ve nested the if conditionals, that will not work in this situation. Instead use completely independent, un-nested conditionals without any else conditions.

 if ( 'de_DE' == get_locale() && ! empty( $german )){
     return $german;
 } 
 if ( 'en_EN' == get_locale() && ! empty( $english )){
     return $english;
 }
 // locale is not English or German to get to this point, it must be Italian
 return '<a href="https://test.sacconicase.com/contatti/">Contatti</a>'.'<br>'.'<a href="https://test.sacconicase.com/agenzia/">Agenzia</a>';