After I've saved a post to a /c hosted by another instance than the one that I'm logged into, I can open that post for editing, but I'm unable to save my edits to that post.
For example: I made a post to !ukraine@sopuli.xyz, while logged in elsewhere. Something or other in the webpage link is forcing a download, so I tried to edit the URL in the post, but I can't save it.
This also happened to a post I made to !coffee@lemmy.world where I was trying to edit the text in the post's Body after saving the post.
I can save edits to my posts to /c's on my native instance just fine.
It looks like some kind of fix was implemented after my post, so I can't replicate the problem for you.
Whenever I edit one of my cross-instance posts, the language defaults to English, and I can save my edits with no issues.
Now whether the fix was on an instance basis, i.e. config changes, or in some Lemmy-system update, I can't tell you.
edit: Maybe my issue was solved along with the fix for the default languages: https://lemmy.ml/post/13410320
We didnt make any changes to the Lemmy version running on this instance during the past week. So it must be something else...