
One proper way? No. A broad set of rules and conventions that have to be followed for the most part? Absolutely. If I had a Chinese 11 year old’s understanding of Mandarin and tried to write a research paper in Chinese, then they would rightly reject that paper since it wouldn’t be in line with the language
But we do need a standardized system for academic writing. All writers in a field need to be able to understand each other. The use of too much slang or different grammar conventions will reduce capacity for understanding, thus decreasing the value of academic writing as a way to spread information.
There literally is improper language though. If I don’t use the correct verb tenses, modifier placements, and conjugations in my sentences, then they are poorly written sentences. A language with no rules is simply not a language. Every language has conventions, and I don’t think any language is better than another, but there is absolutely “proper” and “improper” within the same language, in every language.
The English dialect most often unfairly treated as “improper” in the United States is AAVE. It has a different grammar structure than standard white English. That’s not due to “improperness.” That is just the grammatical systems of African languages being carried through into an Africanized English dialect. But it’s treated as improper because it’s lower class.