Given this, I think the answer is probably “you don’t.” You either tell them to use Julia, in which case you should probably think really hard about your learning objectives when it comes to the code parts of your lessons, or you should stick to teaching the domain-specific stuff, and let them figure out the code stuff on their own.
When I say “think hard about the learning objectives,” I mean that you want to state explicitly (to yourself if nowhere else) what it is you want students to learn, then make you can assess that, and make sure you’re modeling it and giving plenty of practice and feedback.
For the most part, IMO, trying to convince students of things is a lost cause. You can share your excitement and hope some of it rubs off, but if you really want students to learn a thing, you need to explicitly teach it.