The following limitations apply for adding knowledge bases:
Oracle supplies knowledge bases in English and French only. You must provide your own thesaurus for any other language.
You can only add knowledge bases for languages with single-byte character sets. You cannot create a knowledge base for languages which can be expressed only in multibyte character sets. If the database is a multibyte universal character set, such as UTF-8, the NLS_LANG parameter must still be set to a compatible single-byte character set when compiling the thesaurus.
Adding a knowledge base works best for whitespace delimited languages.
You can have at most one knowledge base for each NLS_LANG language.
Obtaining hierarchical query feedback information such as broader terms, narrower terms and related terms does not work in languages other than English and French. In other languages, the knowledge bases are derived entirely from your thesauruses. In such cases, Oracle recommends that you obtain hierarchical information directly from your thesauruses.
Oracle Text Reference for more information about theme indexing, ABOUT queries, using the CTX_DOC package, and the supplied English knowledge base