[schoen]

Backticks were fairly important for shell scripting in the past, but have officially been replaced with $(), which can be nested.

My intuition is that Perl would be the most challenging on a keyboard where it's harder to type unusual punctuation, since it feels like a very punctuation-heavy language, but I don't know whether it actually uses more than C (I think the backtick has a shell-style meaning in Perl too).