@scootergrisen ,
My guess is that Don won’t bother with that in the GitHub area (though you would have to ask him, not us, because we’re not Don and Don doesn’t read most of what happens in the Forum). I am pretty sure he created this “Translation” section of the Forum so that such interactions would occur here, in the “Translation” section of the Forum, rather than having a “perpetual issue” open in GitHub for discussing translation changes.
Probably the best you could do would be to create a topic here called “Collaboration for Danish translation”, and then add a link to that page as an XML comment (like <!-- please discuss any changes at https://community.notepad-plus-plus.org/topic/##### before submitting a PR to change this translation -->). It wouldn’t be enforceable, but there would at least be a notice.
addendum: also, since there is currently an open PR for the Danish translation, I would suggest commenting on that PR that you’d like to talk about the changes together.
And requiring that you get the buy in of a previous translator is likely to never be enforced, either – when someone doesn’t submit a translation for a year or more, despite multiple releases of Notepad++ in the intervening time, all of which change the GUI in ways that there are more strings to be translated, it can easily be concluded that someone has abandoned their translation efforts.