That test is actually nonsense. You can't use unicode characters in URIs without percent-encoding them. And it only worked by coincidence in Erlang < 17.0; the file was UTF-8 but Erlang read it as latin1, sending a "latin1" URI that webmachine/mochiweb then accepted. But Erlang 17.0 breaks this working-by-coincidence since it now forms a URI with Unicode chars in and refuses to make the HTTP request.