Form Submission and i18n seems to have good coverage of this topic, and the Encode::Supported perldoc has this choice quote, which seems to about sum things up:
it is beyond the power of words to describe the way HTML browsers encode non-ASCII form data.

In reply to Re: How do I know what encoding was used for form input? by sgifford
in thread How do I know what encoding was used for form input? by ehdonhon

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