Filter Hook – user_profile_user_gender

You can add your own gender string by filter hook as following

function user_profile_user_gender($gender){
$gender['new_gender'] = array(
'title'=>__('New gender', USER_PROFILE_TEXTDOMAIN),
'icon'=>'<i class="fa fa-female" aria-hidden="true"></i>',
);	
return $gender;
}
add_filter('user_profile_user_gender','user_profile_user_gender');