I've tried to put a summary on this issue together and just
uploaded a first version on my site:
http://www.jodelpeter.de/i18n/fbarch/selecting_charset_and_collation_in_firebird.html

I didn't try to hide my preferences and judgements but hope it
nevertheless is usefull, both as a guide to the current situation
and as an input for future developments.

Please make any factual error known.

Regards,
Peter Jacobi