How can you prove that the set of all languages that are not recursively enumerable is not countable?

One way to prove that the set of all languages that are not recursively enumerable is not countable is by using a diagonalization argument. This involves assuming that the set is countable and then constructing a language that is not in the set, leading to a contradiction. This contradiction shows that the set of all languages that are not recursively enumerable is uncountable.