Shouldn't it be an exception rather than a warning? The fact that an
exception can be downgraded to a warning (and thus involuntarily
silenced) is a bit disturbing IMHO.

Another possibility would be to display the warning, and *then* to
encode the exception message again in "replace" or "ignore" mode rather
than "strict" mode. That way exception messages are always displayed,
but not always properly. The ASCII part of the message is generally
useful, since it gives the exception name and most often the reason too.