There is an edit summary limit in both wikitext and VE, though VE displays it better (decreasing number in bottom-right of "Save your changes" dialog next to "Watch this page").

I don't think there is any truncation on the RC page itself. It seems like the issue is that wikitext editor should display the edit summary limit better (but that might be fixed in the new wikitext editor anyway).

Per triage and follow-up, for the "Cut in the middle of the word without any indication to the user", the RecentChanges page is not doing anything. It is just displaying the already-limited text in the database.

As I suspected (see above), the user is already warned properly about this on the new wikitext editor ("New wikitext mode" in Beta Features) and on VisualEditor. I've filed it for the old wikitext editor as T159303: Show user number of remaining characters allowed for edit summary .

"No wrapping for a comment without word separators" is as @Etonkovidova described. This could perhaps be fixed easily with:

word-break: break-all;

I'm not sure the exact default behavior and about possible side-effects of that change.

I'll narrow this task to that part.

Also, I verified there is no two-line limit.

I've tried fixing this and made some changes in the "span.comment" element. Adding

display:inline-block;
vertical-align:inherit;
width:30%;

Fixes this issue.
PS:I'm not sure about the other possible effects of this.

In T158725#3927226, @lakshay234 wrote:

I've tried fixing this and made some changes in the "span.comment" element.

@lakshay234: Thanks for taking a look at the code!
You are very welcome to use developer access to submit the proposed code changes as a Git branch directly into Gerrit which makes it easier to review them quickly and provide feedback. If you don't want to set up Git/Gerrit, you can also use the Gerrit Patch Uploader. Thanks again!

Change 743572 had a related patch set uploaded (by TheDJ; author: TheDJ):

[mediawiki/core@master] Very long words in editcomments should wrap

https://gerrit.wikimedia.org/r/743572

Change 743572 merged by jenkins-bot:

[mediawiki/core@master] Very long words in editcomments should wrap

https://gerrit.wikimedia.org/r/743572

This is still a problem for the RC/watchlist modes which use tables. I also don't really see a solution to that, which does not include "remove tables".

In T158725#7551584, @TheDJ wrote:

This is still a problem for the RC/watchlist modes which use tables. I also don't really see a solution to that, which does not include "remove tables".

I just tested this -- if we add word-break: break-word; it covers the case of comments inside tables.

I'm not ENTIRELY sure if I can remove the overflow-wrap without having regressions for the other cases, but it seems that adding the three seem to cover the cases (some apply in different contexts).
Patch incoming -- I added a comment that may clarify why there are multiple seemingly related rules.

Change 920683 had a related patch set uploaded (by Mooeypoo; author: Mooeypoo):

[mediawiki/core@master] RecentChanges: Apply word-break to comments that are inside table cells

https://gerrit.wikimedia.org/r/920683

Change 920683 merged by jenkins-bot:

[mediawiki/core@master] RecentChanges: Apply word-break to comments that are inside table cells

https://gerrit.wikimedia.org/r/920683