The current 2.2.0 release also includes:

# Used to determine what language should be used by the
# indexer above. Applies to Xapian and PostgreSQL native-fts
# indexer. It sets the language for the stemmer, and PostgreSQL
# native-fts stopwords and other dictionaries.
# Possible values: must be a valid language for the indexer,
# see indexer documentation for details.
# Default: english
indexer_language = english

in config.ini. My suspicion is that this problem would be handled by using
the Chinese language/locale for xapian, but it might not be enough.