What level are your students (primary school, high school, technical college, university)?

You said it's not a core skill, so what is their core skill? IT? Machinist? Electronics engineer?

C is an excellent "fundamentals" language that anyone with a software engineering and maybe computer science should have exposure too, but if their programming is purely practical (e.g. scripting for IT?) C is essentially irrelevant.

Javascript is very narrow in scope but if they're web designers then it's essential.

I'll back the other commenters that if they need a language they can do useful things in (e.g. simple automations, calculations), Python is hard to pass over.