it's not a formal nor complete language because it has so...
CMV: There should be a universal sign language the whole worlds learns in school or by parents.
In this case your entire view is flawed because this already exists. ISL, international sign language. it's a pigeon language used at international conventions such as the World Federation of the Deaf congress. It's a mish mash of different sign languages from across the globe designed to help communicate simple concepts. it's not a formal nor complete language because it has so few official signs, it is a pigeon language and where the limitation of official signs becomes an issue, conversational partners often bridge the gap with a common sign language from a shared sign family, almost like a linga franca (for example, I don't know NZSL, but because Auslan and NZSL both borrow signs from BSL, I can hack my way through a conversation with a New Zealander by avoiding Auslan specific signs and using borrowed signs). ISL is recognised as a valid sign language because of it's use in international deaf events. It's also sometimes used by deaf tourists who require an interpreter while travelling. But it's incomplete, it's only helpful for survival, it is doesn't assist humans to truly connect on a deeper level the way a fully fleshed out language does.