O. k. One more question (perhaps someone reads it).
Sometimes, hyphenation ist refused because of unknown language. To verify the language by the plugin, is there the entry in the <head> part of the source code relevant, such as <meta content="en" scheme="DCTERMS.RFC4646" name="DCTERMS.language"/>? - Given the case, I could insert it via Sigil or Note pad++, or not?