@Mad Max: Thank you, this worked for me. But what is the difference between "partner" and "user"? Why does Odoo uses "partner" as default, and not "user"?

Thanks Jennish I'll give that a try.

Diden't work so ....:
Took a very deep breath did a backup of my odoo directory.
Did a git stash of my changes to the Danish translations

And did a git pull

Restarted the odoo server service

Now they work :-)

No clue what has been fixed, but they work :-)

Now I'll try and incorporate my translation changes again

In email template under settings tab
set language as {{ object.user_id.lang }}