Let's suppose I have a form asking name and email. I want to sent a confirmation mail, so I put {email} to "Send basic admin notification email to:" -field and put "Hi, {name}, thank you..." as email template. That works.

Now, if I also ask preferred language from two possible, I guess I can use something like {if(email=='en', email, '')} as basic admin notification, and {if(email!='en', '', email)} as detailed admin notification email.

But this does not scale for more languages. Is there anything I could do? Some kind of redirection trick?

You could place the email content in an equation type question. This could be tailored for each language. Then in the basic notification template, simply reference this question.

Nice and simple. Thanks!

Still a problem: it seems that the email formatting is lost, i.e. referring to "confirmationen.NAOK" does not give the HTML as shown in the question editor.

confirmationen.question to have the HTML content.

Than you can use a text display question

Ah, of course. Thanks!