Where are you using the substitute function? It should be in the auto enter tab, calculated field-of the Article field, with the box "Do not replace existing value..." unchecked
Make sure it looks exactly (English) like this:
Substitute ( Self ; "," ; "." ) //you had substitute spelled wrong and had a : (colon) instead of a ; (semi-colon) after Self.
Also you have to allow auto enter calculations during import
It works beautifully, unchecking the "Do not replace existing value " did the trick. FM had corrected my typos already.