I’m not sure I follow you. The distinction between an onsite and an offsite resource isn’t cultural. You can configure Discourse to open external links in a new tab, but some users will find that annoying. A popup warning the user that they are about to go offsite (regardless of if via a new tab or replacing the current) would annoy most users.
In your own post above you link to an offsite resource (Telescope). It’s highlighted in blue, has an indication of how many people have followed it from your post, and the cursor changes when you hover over it:
Is this what your users find confusing?
Many of our users took a while to grock how much information is presented by the Discourse UX. If you explain the meaning of the various elements then most users will figure it out. Some will not be interested in what they see as “fluff”, others will feel more at home. At a “soft” level the problem is that people are disconcerted by not knowing, so the grey circle with a 6 in it may bother them until they know what it indicates. Once you’ve explained what it means then the discomfort goes away, even if they aren’t interested in the least to know how many users have followed the link.
The slider on the right is a masterful piece of UX. (It’s at the level of IKEA assembly instructions.) in the sense that it presents a large amount of information and reacts dynamically to the thread/screen without getting in the way. Not everyone wants to know the details, and that’s fine, but most people will benefit from a tool if you show them how to use it.
Years ago I was running inhouse IT for a medium size business. I needed to book a flight, and I happened to be near the office of the secretary who handled that, so I dropped into her office. I explained where I needed to go and when, then watched as she opened a word document, scanned through it until she found the country I was going to, then retyped the airline URL (by hand) in her browser.
I took a moment to explain copy/paste, google, and bookmarks, and walked through a few examples with her. When we were done she said “You must think I’m terribly stupid.” my answer was “Not in the least, if anyone is stupid it’s whoever didn’t explain the most basic aspects of the technology with which you do your job, or decided that merely purchasing the kit and putting it on your desk was all that needed doing.”
Training/explaining is still necessary, regardless of how intuitive a UX is.