I think there are two scenarios and they need different messages:
latest tab is empty (I think @justin suggestion of “You’re all caught up! Ready to [start a new conversation]?” is a good one here.
New category is empty (or site is brand new, etc). This one needs more of an exhortation to create some topics so people have something to talk about, and real actual topic examples of what the category is for (other than the category description)
How would scenario 1 happen:
out of scenario 2 cases ? (EDIT: Oh, maybe by selecting TAGS !?)
There also is the “show tracked or watched topics” talked about above, but is “you’re all caught up…” the right message for this case ? (scenario 3 ?)
I put together a PR for this. The message is
You’re all caught up! Ready to start a new conversation?
Does anyone know – is there a Plugin or Theme Component or config setting for this (yet 
)?
Alternatively, can it be edited somehow through js.topics.none.latest or in the config/locales/client.en.yml
Just visit /admin/customize/site_texts and search for “that’s sad”. You can change it to whatever you want.
EDIT: Though it looks like “that’s sad” has been changed in core. Looks like it’s just this now:
bottom:
latest: "There are no more latest topics."
posted: "There are no more posted topics."
read: "There are no more read topics."
new: "There are no more new topics."
unread: "There are no more unread topics."
unseen: "There are no more unseen topics."
category: "There are no more %{category} topics."
tag: "There are no more %{tag} topics."
top: "There are no more top topics."
bookmarks: "There are no more bookmarked topics."
Thank you so much @pfaffman – I am also very glad to learn about your Discourse Support Services!
You can also change the message to fit the category with the “after” pseudoclass :
.category-next-events .topic-list-bottom::after {
content: ‘No event for the moment’;
}.category-next-events .topic-list-bottom .footer-message {
display: none;
}
You may add language pseudo class if you have a multilingual site.