Quoting this post at UBBDev
Originally Posted by Gizmo
As for your issue with converting to UTF8, aren't some of the characters used on your forum multibite? If so, you can't just move over to UTF8 as it doesn't support those characters. We've written a Wiki article regarding this issue at UTF-8 vs Latin-1 (ISO-8859-1), which also has links to several character set related issues.

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