I have finally got around to trying the OpenOffice plug-in. It works very well and is now my favourite tool for conversion to fb2 format.
It installs in English (sort of, I think they used google to translate the text). I found the Help file not helpful in getting started, there's too much unnecessary technical detail and my eyes glazed over on page 2

It might describe the plug-in's capabilities in detail and might be interesting to developers, but I really don't need to know or particularly care ...
Basically what I did was the following:
- Installed the plug-in via OO Extension manager
- Opened the ExportToFB21_Test-1 document that comes with the plug-in and saved it as a styles template
Now when I have a text I want to convert to fb2 all I do is:
- save it as OO document (whatever.odt)
- run the OOFBTools Text corrector ( I've played around with the options and pretty much use all of them except the first box - removing breaks for hyphens - and collecting lines of paragraph broken by symbol)
After the clean-up I search and replace chapter name formatting. I load the formatting styles from the saved template. I like to have a TOC and proper chapter navigation in the file, so I replace whatever format was used for chapter names by a style called Level 1 from the template.
That's pretty much all. I then export it to fb2 and to make sure the file validates I fill in the following:
- book title
- language
- book author
- genre
Using the plug-in for conversion is really easy and takes about one tenth of the time it took me to convert a file when I was using Book Designer.
Many thanks to the developer.