I'm not really sure what else the message should say. If we talk about parsoid, the user will be pretty confused. Are there any suggestions?

Perhaps call it the "editing server"? As in "Sorry, we could not save your changes to the editing server" and "Sorry, we could not get a copy of the page from the editing server" etc.?

Change 157775 had a related patch set uploaded by Jforrester:
Add debugging help to VisualEditor

https://gerrit.wikimedia.org/r/157775

Change 157775 merged by jenkins-bot:
Add debugging help to VisualEditor

https://gerrit.wikimedia.org/r/157775

With the above patch, the former message:

Error loading data from server: parsoidserver-http-bad-status:
500. Would you like to retry?

… turns into:

Error loading data from server: parsoidserver-http-bad-status:
500: Page Fetch failure for "BADURL": Error: getaddrinfo
ENOTFOUND. Would you like to retry?

Which is not ideal, but at least describes things a bit.

I just hit this message (was about to reported a semi-dupe) on enwiki. I got the below variant:

Error loading data from server: parsoidserver-http-bad-status:
404: No pages were returned from the API request for $article.
Would you like to retry?" (yes/no)

I hit yes and it worked. So... why not just retry without asking me first?

If it fails again (or for X times, whatever) then give a more generalized "ooops, sorry 'bout that" message with a "click here for more info" dropdown (with the message I just pasted, minus the "would you like to retry?" bit, of course).

For what is worth, Catalan Viquipedia users confused about an error message from Parsoid:

Alguna cosa no ha funcionat

parsoidserver-http: HTTP 500

Descarta

"Something didn't work" :)

https://ca.wikipedia.org/wiki/Topic:Shssmsofmcgkqhmv

I agree that "Something went wrong" isn't very helpful. What would be helpful is an explanation of what to do. For example, if it's hopeless and you've just lost all of your work, then acknowledging that it's hopeless would save people the time and stress of trying to save it.