Just a reminder that sign language is not a language. It's a GROUP of languages.
There are over 300 sign languages currently used and many countries have their own sign language. Some even have multiple!
Here in Canada, American Sign Language (ASL) is the most common one but there's also LSQ (Langue des Signes Québécoise), Maritime Sign Language, and PSL (Plains Indian/Indigenous Sign Language) - which is an Indigenous sign language. There are also other Indigenous sign languages used in Canada such as Plateau Sign Language and Inuit Sign Language - though unfortunately, despite revitalization efforts, both (and honestly PSL to an extent) are dying out.
Even within sign languages such as ASL, there are different dialects, accents, slang, and other differences between regions. LSH (Lange des Signes Haïtienne), for example, is a variant of ASL used in Haiti. Other dialects of ASL include MSL (Moroccan Sign Language), NSL (Nigerian Sign Language), and SgSL (Singapore Sign Language).
These sign languages were originally brought to these countries/regions by ASL users (such as American Peace Corps volunteers in Morocco) and have since evolved into their own separate dialects and, in some cases, their own languages entirely. It is worth noting that a lot of these countries did have their own sign languages before this, many of which are not documented and have been largely "replaced" (for lack of a better term) by these dialects. There is a strong history of colonization and racism here, which should be considered when talking about the history of sign languages. Within the US, BASL (Black American Sign Language) is also used - this evolved as a variant of ASL due to the race-based segregation of schools.
Outside of these dialects, there is also a difference in how people sign even within the same language/dialect. For instance, the way that somebody from America signs the word "gray" is completely different from how we sign it in Canada. Similarly, I've even found that the letters "M" and "N" are signed differently within Canada.
The way somebody signs can also differ from region to region. I'm not talking about specific grammar rules or words/signs but just the general way somebody signs. When I sign, I've been told I sign with an East Coast Canadian accent. It isn't something I personally notice, but it is something people have pointed out to me a lot. This is because I learned ASL from my mother, who was born in Nova Scotia. I've also known people from the south of the US who sign with a kind of... drawl, for lack of a better term. Similarly, I've met people from New York who sign super quickly and have a particular sort of rhythm with their signing. I've also met people with limb differences whose signing was affected by that, giving them their own sort of unique accent. Something else that's particularly interesting is that a lot of Deaf gay and otherwise queer people I know tend to sign in a very particular way with much more "exaggerated" (for lack of a better term) facial expressions and rhythmic signing.
This has all been in relation to ASL just because that's what I grew up with and what I'm fluent in. Although I do know some PSL and LSQ, I'm not nearly as familiar with them. That being said, this is all still true of other sign languages like BSL (British Sign Language), CSL (Chinese Sign Language), LSF (Lange des Signes Française), and hundreds of others.
This post was made because I keep seeing people say stuff like "I'm learning sign language" or saying that their character "speaks sign language". This is something that is a personal pet peeve and bugs me greatly. It's one thing to say it IRL (where the language you're referring to is generally known based on what your region uses) but online or in media with a wider range, it's a different story.
This may not seem like a big deal and, compared to other issues, it isn't but it does contribute to the portrayal of Deaf people and sign languages as a monolith and it erases the long history and diverse cultures of different sign languages.
So to summarize: Sign language is not a language. It's a massive group of individual diverse languages, each with their own rules/guidelines, practices, and quirks.
Individual sign languages, however, ARE languages. This may seem obvious but there is a long history of sign languages being dismissed as "not being real languages" or "just being gestures" so I want to make this point abundantly clear.