What do I have to do to make AjaxSearch snippet to search chinese character contents?
If you use an utf-8 encoding, nothing else.
See this
short document with Kanji characters. and try to search something like 情 on
this demo page.
I haven’ tested with traditional chinese characters. But to test the sql order executed by AS with your owns document, substitute the 情 character in the following sql order. Try this sql order with your own database by using phpMyAdmin. And let me know if you get results.
SELECT sc.id, sc.pagetitle, sc.longtitle, sc.description, sc.alias, sc.introtext, sc.template, sc.menutitle, sc.content, sc.publishedon, GROUP_CONCAT( DISTINCT CAST(ntv.id AS CHAR) SEPARATOR "," ) AS tv_id, GROUP_CONCAT( DISTINCT ntv.value SEPARATOR ", " ) AS tv_value FROM `mod2_site_content` sc LEFT JOIN( SELECT DISTINCT tv.id, tv.value, tv.contentid FROM `mod2_site_tmplvar_contentvalues` tv WHERE (((tv.value LIKE '%情%'))) ) AS ntv ON sc.id = ntv.contentid WHERE ((sc.id IN (63,308,64,65,66,67,68,69,70,71,72,73,97)) AND (sc.published=1) AND (sc.searchable=1) AND (sc.deleted=0) AND (sc.type='document') AND (sc.privateweb=0)) GROUP BY sc.id HAVING (((sc.pagetitle LIKE '%情%') OR (sc.longtitle LIKE '%情%') OR (sc.description LIKE '%情%') OR (sc.alias LIKE '%情%') OR (sc.introtext LIKE '%情%') OR (sc.menutitle LIKE '%情%') OR (sc.content LIKE '%情%') OR (tv_value LIKE '%情%'))) ORDER BY sc.publishedon,sc.pagetitle
For your information the sql order is catched and displayed
on this page as soon as you run a test on the demo site.
By the way, I was wondering can I use the AjaxSearch to search content on my custom tables in Modx? 
Is it going to take some work? Thanks for your quick response.