In order to allow all communication to be sent in a chosen language, a 'lang' field is added on the event.event model. If set (amongst the installed languages) this language will be used to translate email templates instead of the partner's one (which is still the default one) The field is added on the event form view. Task-3357099 closes odoo/odoo#127540 Signed-off-by: Stéphane Debauche (std) <std@odoo.com>