You can call yourself polyglot when you are independent. Independent in the sense, you are responsible to answer if anything goes wrong either on server, backend or fronted side. Organization you're working with can assign you whole project without involvement of other dev
You are polyglot if you can handle team of fullstack dev. That means, you have to be fullstack with multiple programming skills.
Fullstack: python(django), react, mysql, aws, linux(ec2)
Polyglot: php, java, python(django), react, mysql, aws, linux(ec2)
Hope this makes clear about these two terms 😀