For example page is created in the Windows-1251, but does not have the appropriate tag, and FESS is trying to bring in UTF8 encoding
Fess uses a charset info of a meta tag.
The default is UTF-8 if it’s not specified.
If you want to change it, add charsetName to apps/WEB-INF/classes/crawler/transformer.xml:
... <component name="fessXpathTransformer" class="org.codelibs.fess.crawler.transformer.FessXpathTransformer" instance="singleton"> <property name="charsetName">"Windows-1251"</property> ...