> Because sign language is the most literal thing you can think of. If I look at someone and point to them, then point to someone else, what do you suppose that means? The only issue is local dialect/slang which is easy enough to figure out.
I asked someone who was studying ASL about the differences between sign languages. She pointed out that they do commonly have different signs which might be very abstract and non-literal, often because they arose in different schools for deaf people (or different regions with a very high incidence of deafness) in earlier eras.
However, some of the sign languages have some etymological relationship with one another, especially French Sign Language (LSF)
Those relationships might be something that reinforces the impression that all sign languages are inherently related, but there are also sign language isolates that don't have an etymological relationship to other sign languages (although if they've had later contact with other sign languages, they could have loan vocabulary or other contact influences).
Edit: I don't mean to suggest that people who know different sign languages couldn't communicate at all, but I expect that someone who knows one wouldn't be able to understand a signed conversation between native signers of an unrelated one.
Join a Facebook group called "Deaf World Love Sign Language V.I.P" (signers from all over the world. can't even comment in the same language)
If you know sign language, you can pretty much understand what they're saying. The first time I noticed I understood someone in Brazil, talking about work, I didn't notice that... I was understanding them. I didn't understand certain stuff -- slang --.
Yes, abstract and non-literal. It's because of the PC brigade. Growing up... things were a whole lot different. It's still pretty much literal.
Edit: oh, there's already a special Swadesh list for comparing sign languages because of "overestimation of the relationships between sign languages, due to indexical signs such as pronouns and parts of the body". (Those signs are the ones that are most likely to be shared because they're likely to arise independently or have an inherently obvious meaning.)
I asked someone who was studying ASL about the differences between sign languages. She pointed out that they do commonly have different signs which might be very abstract and non-literal, often because they arose in different schools for deaf people (or different regions with a very high incidence of deafness) in earlier eras.
However, some of the sign languages have some etymological relationship with one another, especially French Sign Language (LSF)
https://en.wikipedia.org/wiki/French_Sign_Language
https://en.wikipedia.org/wiki/Sign_language#Classification
Those relationships might be something that reinforces the impression that all sign languages are inherently related, but there are also sign language isolates that don't have an etymological relationship to other sign languages (although if they've had later contact with other sign languages, they could have loan vocabulary or other contact influences).
https://en.wikipedia.org/wiki/Category:Sign_language_isolate...
Edit: I don't mean to suggest that people who know different sign languages couldn't communicate at all, but I expect that someone who knows one wouldn't be able to understand a signed conversation between native signers of an unrelated one.