I think it’s important to be able to read the host language and be familiar with its idioms, and of course the ease of doing that scales up with ones reading proficiency in the host language.
I think the most Java I’ve written in a Clojure context was some throwaway code demonstrating a minimal example of a bug in a Java package over which I maintain a Clojure wrapper. The Java was only necessary because I wanted to literally “speak their language” when reporting the bug.
I think it’s quite rare for Clojurists to write any Java for their Clojure projects. Have you found it necessary?