I would just answer "Nothing."

Because, really, it isn't just because a language has it's deficiencies that I would want to change that. That would probably result in a new language, which is not desirable. Usually a language is what it is because of it's pros, which unfortunately happens to create the cons. If you remove the cons you would probably also lose some of the pros.

So, I think a better question would be: "And what wouldn't you use [language] for? Why?" Or, if you want to sound cool, "What do you hate about it?"