It is not necessary. many experts of English do not have certificates and they are also fluent in English. even many who might learn in itself so it does not need that kind of thing. Furthermore, it may be the manager also does not want to struggle to see it one by one.
There are two possibilities for this because I know that cryptocurrency covers the whole world by uniting languages, namely English.
1. It must be difficult to have a certificate because the bounty is only followed by anyone who wants to campaign, if such initial intentions are definitely discrimination.
2. It is also good to have a certificate because English is needed and KYC can also say it.