People who can neither hear nor speak (that is,deaf and dumb

这里（that is,deaf and dumb people）是插入成分,对前面的进行解释说明,所以加了括号.
完整的翻译：既听不到又不能说的人,也就是聋哑人,依靠他们的手指相互交流.
People who can neither hear nor speak talk to each other with the help of their fingers.
主语 people ,谓语 talk,to each other 作宾语
再问： each other 是什么短语
再答： each other 代词，意思是相互