If the community is on your local instance, it doesn’t show the instance in the dropdown. If it’s a remote instance, it does.
However instead of using the actual unique URL of the community, it uses the display name. So in this case lemmy.ml/c/ireland and lemmy.ml/c/ireland_on_lemmy both have their display name set to just “Ireland”.
I think differentiating between local and remote communities is actually pretty useful but obviously the second thing is a problem when you’ve got competing communities on one server. Which I guess is a thing that people are doing.
Maybe instead of:
Ireland
Ireland
it should be showing
Ireland (/c/ireland)
Ireland (/c/ireland_on_lemmy)
which not only fixes this problem but also means you can see how to get to a community to go check it out before posting there (this comes up sometimes in the process of crossposting) and it’ll stop, say, a mod giving their community an unrelated name to confuse people into posting something inappropriate or whatever.
There should probably also be a character limit on the display name because that UK one is obnoxiously taking up all of the horizontal space and leaving no room for its actual identifier.