A form was submitted in the %S encoding which cannot encode all Unicode characters, so user input may get corrupted. To avoid this problem, the page should be changed so that the form is submitted in the UTF-8 encoding either by changing the encoding of the page itself to UTF-8 or by specifying accept-charset=utf-8 on the form element.
Cafodd ffurflen ei chyflwyno mewn amgodiad %S nad yw'n gallu amgodio'r holl nodau Unicode, fell gall mewnbwn defnyddiwr gael ei lygru. Er mwyn osgoi'r broblem hon, dylai'r dudalen gael ei newid fel bod y ffurflen yn cael ei chyflwyno mewn amgodiad UTF-8 un ai drwy newid y amgodiad y dudalen i UTF-8 neu drwy bennu accept-charset=utf-8 ar elfen y ffurflen.