Hello again UncleCheese!
So I've been stupid enough to try using Translatable on normal data objects and not just the SiteTree. Generally this actually works when used with a fix someone posted but in one scenario it breaks down. If I switch translations through the translation tab then DOM/CTF stops working.
What happens when you switch translation through the translation tab is that the URL becomes for example http://localhost/fkg/admin/show/26/?locale=en_US instead of just http://localhost/fkg/admin/?locale=en_US. Everything else I've checked seems to be ok (the locale is set properly for example) so I'm right now thinking it has something to do with the URL. I checked the URL on the iframe in the popup and it's the same URL as when it's working so I have no clue as to where to start looking.
Do these can't handle sub-URLs errors happen in some kind of central place that you can point me to or are they really hard to find/debug? If you can point me to the general area I would be more than happy to try to fix this, right now it feels kind of hopeless since I don't even know where to start.
Kindly,
Marcus