Lack of support for non-Latin text
FDSE is designed to search languages that use the Latin character set, including English, German, and Dutch.
Languages that use other character sets may not work properly, including Greek, Hebrew, Russian, Japanese, Chinese.
Support for non-Latin languages is on the list of feature requests. See CGI Resources for search engines that already work properly with those languages.
"Lack of support for non-Latin text" https://www.xav.com/scripts/search/help/1001.html