Bonjour peu de personnes utilisent swift ici ça va être difficile de t'aider.
Mais 10 secondes de google search avec le ligne "app_swift.c:337 app_exec: Failed to set voice" donne l'indice:
Is there a swift.conf file in your /etc/asterisk directory?
Does it include an entry for the voice you have registered??
voice=Allison-8kHz