Somewhat offtop, but I wanted to ask: how much universal intelligibility there is in sign languages? I understand that sign languages are, well, languages, and thus not readily inter-intelligible. But so are, perhaps, our native languages, yet here we are speaking English. And not just because this is a somewhat SV forum: english is just internationally popular right now. Of course, most people I meet don't really speak english, and lingua franca will change based on the region (at many places most people will know nothing but local language), but learning english is still way more practical worldwide (outside of USA and UK) than learning estonian, and speaking english I have good chances to be understood in most big cities in Europe and worldwide.

Also, I understand that it's hard to compare, because most people don't speak any sign languages, but is there something similar with sign languages?

Honestly, I feel weird desire to learn some sign language, but there's absolutely zero practical reasons for me to do so, and I wonder if learning, say, ASL, could help me interact with deaf people in my country or somewhere else. Sure, I won't understand them when they speak their local dialect, but is there something common that most deaf people would probably understand?