CouchDB is written in C++ but was replaced by Erlang. It is a concurrent, functional programming language mainly focuses on fault tolerance (Erlang programming language also used for build massively scalable soft real-time system with requirements on high availability).
Some of its parts are written in C language too. As we know that CouchDB supports view server and the views (form map or reduce) are written in JavaScript per default (but can also be written in Erlang). Therefore CouchDB requires the JavaScript engine SpiderMonkey (which is written in C language).
