You will most likely either need to look at the Content-Type header of your form submission request or, if that fails, guess. I think in the past browsers used to submit form data in the same encoding as the page the HTML form was on, but I hope that nowadays with fairly recent browsers, they always send the content characterset/encoding with the request:
Content-Type: text/html; charset=utf-8
Ideally, your framework already looks at that and uses the appropriate Encode::decode call, but I'm not sure what your users browsers actually send and whether that can be decoded without problems. Maybe seeing some more of the code that receives the input and of the HTML that is used to display the FORM to the client can help us narrow the problem down somewhat.
