This proposal has been rejected. This decision was taken by the language committee in accordance with the Language proposal policy based on the discussion on this page.
The closing committee member provided the following comment:
not a natural language and not recognised in ISO-639-3
Yerkish is a signed language. It has its own script. The Yerkish language is pretty limited due to its application and scope. Since it is used in scientific research, in primatology and also by computers,it is nice help, sort of, to have that Wiktionary available for scientists and interested public to look up Yerkish terms and expressions, and document them online. ISO codes for Yerkish (language and script) are requested. This process may take time.