I was going to ask in the other thread if there were any database changes involved and this suggests that there are. Your last message seems to indicate there are results returned by default without the alternative parsing so that would point to the issue being related to the non-standard changes applied.
Unfortunately, this simply isn't something we support. If you are making changes to the database like this, there may be custom PHP changes required to change how the search strings are passed to MySQL. I'm not familiar with full text search using the ngram parser, so we can't really comment on that.
XFES is not "developed" for giant forums. It improves the search results in all forums and provides better performance for large forums. CJK searching is, roughly, an entirely distinct search approach to space-separated/word-based languages and thus alternative approaches may need to be taken. This isn't something that XF officially provides or supports as the default configurations (for both MySQL and Elasticsearch) don't use a tokenization approach that work in these situations.
It's worth mentioning that if you change the min word size in MySQL, you need to rebuild the table/indexes for it to be reflected.
Thanks for your response.
I did rebuild the index after changing the word length.
It looks like by default that XenForo treats two CJK characters as one length unit, according to my current observation.
It's not my site (and the sitemaster is someone in this forum).
Unfortunately he doesn't want our technical relationships being compromised to the
public due to his fear of his commercial competitors.
Our site is using a free distro variant of RHEL and the paid Chinese enterprise version of a webpanel, and that panel doesn't support the installation of ElasticSearch.
I will try all other possible resorts before admitting our necessity of buying XFES (considering its cost of server computing power).