... and here is the solution !
There is a 'bad' code in include/functions/easier_attributes.php, for example in
function GetAttributeOptions($languages_id = 1) {
and
function GetAttributeValues($languages_id = 1) {
This code excludes other languages than id=1. I found '$languages_id = 1' six times in the this file (and complete code) and changed it for me to '$languages_id = 2'.
But normaly this should be dynamic.