Although C probably counted as a modern language back then (after all it's not B) today I think "modern" probably means at least Java and likely something from this century like Rust or Typescript.
"Modern" means "we fixed the deficiencies of the old project and introduced our own". When I read "modern" I understand it's likely to be a variation of the second system effect [1]. When it's not just advertisement/PR BS.
When it's part of a request, it generally means "I don't know tech XYZ but I'm pretty sure I could enjoy it and contribute if it was using a tech I know". Which is generally a form of procrastination.
I dislike Javascript and I don't know Objective-C, and it didn't prevent me to tinker with Oolite, which uses both, because I like the game (now, tbh assembly is "hardcore" so OP's request is legitimate).
