Thanks for the background and suggestions, that's very helpful.
I'm gradually learning Clojure with no Java experience. In this case I was searching for the preferred Clojure way to access items in directories declared under :resource-paths in a Leiningen project.clj file. Perhaps clojure.java.io/resource isn't the best way to do this as it's possibly too tied to the expectation for a URI instead of a more general IRI.
You're suggested workaround did work for my use case:
(slurp (.getContent (clojure.java.io/resource "abcíd/foo.txt")))
but hopefully there would be more native/direct Clojure way to accomplish the same eventually.
I don't know if java.net.IDN would be useful internally as a fix in clojure.java.io/resource — I'm assuming not since it wasn't added until Java 6.
user=> (import 'java.net.IDN)
user=> (java.net.IDN/toASCII "/dir/déf")
user=> (java.net.IDN/toUnicode "xn--/dir/df-gya")