Korean’s a little different from Japanese in that our language’s hangul writing system is an actual alphabet while Japanese katakana and hiragana are syllabaries. Koreans, in fact, love to go on about the superiority of the hangul writing system as one of history’s greatest achievements; as a linguist it is definitely an interesting development which contrasts favorably with the well-established use of syllabaries in many other Asian countries. But that’s a tangent.
The bottom line is that except when entering Chinese characters, the Korean input method does not require Enter to be pressed to complete a syllable.
But you’ve raised an interesting issue: No hangul autocomplete url_title. Maybe the lack of the URL title is causing the error. I’m going to use English in the Title field, allow the url_title to be autocompleted (or manually enter the url_title), and see if hangul text will be accepted in the other, custom Text Input fields.
What’s strange is that the EE error message isn’t identifying the url_title as being the problem. And, of course, the other strange element is that PHP 5.2.17 works just fine, while only PHP 5.3.6 is a problem.
UPDATE: I’ve confirmed that the problem does not arise from inability to autocomplete the url_title. I’ve manually entered a Roman-lettered url_title, and Roman-lettered Title field, with Korean entered into two Text Input custom fields. On MAMP’s PHP 5.2.17, the Korean entries are accepted. On PHP 5.3.6, ExpressionEngine throws the error that the fields are required—i.e., as if no text had been entered in those fields at all.
Database and table are Unicode. It’s a fresh EE 2.3.1 install (no legacy database), and Kyara tells me all the tables are UTF-8 Unicode.
I haven’t tested this with plain PHP forms yet, but it sure does look like an EE problem to me. I don’t ordinarily have trouble entering Korean text anywhere, and since the problem manifests itself only on EE with a specific PHP version, that points to a coding problem.
I want to test on Windows, in order to exclude the Mac OS X Korean input method, but my VMWare Fusion install recognizes localhost as being in the Windows VM. So complicated!