@Lulu
Thank you for your time and your feedback. When I suggested to play against
Alouette, I forgot that it wasn't included in your installation.

You don't really need
Assistant to use a new engine. You can simply start
Eschecs with engine path as parameter. Or select the engine from
Eschecs menu (if engine path is in the configuration file,
config/linux.ini or
config/windows.ini).
Anyway, congratulation for finding a solution by yourself, and sorry for the inconvenience.
Yes, I have to update the Lazarus project for
Assistant. And I have to remove reference to
Language unit. It's the old translation system. It has been replaced by PO files.