“What about the button “send message”? I’d like to translate the words into French.”
You can use joomla language override with language constant: QX_CF_SEND
“I haven’t tested sending a message yet, and I’m wondering which mailbox will receive the email?”
You need to config the admin email via contact form element first: https://imgur.com/a/eg6DP This email will receive the content of contact form.
To translate text, just open language folder -> en-GB -> en-GB.contact-form.ini