This question can not be fully answered in prose. It can only be answered with a challenge: Learn four or five diverse languages reasonably well, then try to create the single syntax that works well for all of them. You'll understand when you're done... or perhaps rather, when you find you'll never be done.

I will give one example of the tens upon tens of issues you will encounter: What's the one true syntax for a type declaration? Then, once you've answered that, how does that one true syntax manifest in Python/Perl/Javascript?