When using an internal request
_sourceResolver.resolveURI("cocoon:/....")

with parameters, to respect RFC we should encode each parameter using URIUtils.encodeParameter.
But in internal request, the rg.apache.cocoon.environment.wrapper.RequestParameters#parseName method is badly implemented and does not support UTF-8 encoding.
For example the £ character is encoded as %C2%A3 but the parseName method will decode it as ã.