Tentacle Sign Languages

The Ojiongo (squid people) have a native language known as Ogean that is famously complicated. Some say it is deliberately complex as the Ojiongo are secretive and don't like to share their language with outsiders.
The Ogean language often involves signing with hands and/or tentacles to provide emphasis or subtext to spoken words. It was not a giant stretch for some clever squid people to develop a means of communication that involves hand and tentacle movements entirely.
A lot of bioluminescent fish use their glow as a form of communication and some ojiongo have adapted this into their sign language to let them communicate in the dark, either with magical bioluminescence or using a variation of alchemy to mimic natural bioluminescence. This is a necessity for using the language at night or in deeper waters, two situations many ojiongo like to operate in. It also allows for communication across long distances of simple messages in clear dark waters.
Two factors have slowed the spread of tentacle sign language. First, apart from the ojoingo, most Scaraquans don't have the physiology to reproduce it. Second, the ojiongo who use this sign language tend be a paranoid secretive lot and don't like to disseminate knowledge that could be used against them. In a lot of ways, ojiongo are their own worst enemies, so many rival factions have their own words, phrases, and even whole coded dialects that they keep solely within their own insular groups.

Geographical Distribution

This language can be seen almost anywhere where Ojiongo swim, but tentacle sign languages are most commonly seen in the Sea of Taedi which has a lot of deep dark waters and a high population of scheming secretive ojiongo.