We were running into problems on the awakeningthedreamer.org site where international characters were causing an error. The problem was that the form values being sent through JSON were only being run through escape and not encodeURIComponent.
On the PHP side, incoming data needs to be decoded to ISO-8859-1 using utf8_decode unless the database, PHP string functions, and HTML header settings are all UTF-8 compatible.
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In the end, UTF-8 is being stored in the database and displayed via the web.
I had to add the following to HTML header and make sure Apache headers were not specifying the character set.