From your description it looks like you're only willing to affect external links, so:
You could add to your /global.js something like this (or your /common.js if you want this to only be applied in specific wiki(s)):
/* make all external links open in a new tab */ $("body").click(function(e) { var a = e.target; if (a.nodeName.toLowerCase() == "a" && a.href.indexOf(location.origin + "/") != 0) { // user clicked an external link $(a).attr("target", "_blank"); } });
I'm not sure if the use of JavaScript for this behavior matches the customization policy, as i haven't made any public wiki scripts in a few years. If you are an admin there, you could ask a Wikia staff member to enable such behavior.
However, note that if a reader wants to open a link in a new tab, they could do just that whether they are in pc or mobile. Maybe it's just my opinion, but sites don't let me open a link the way i want really grind my gears.