the good thing with Wordpress is, that it allows one RSS Feed per Category.
So to avoid a language mix we could add one category for english and assign
all english entries in addition to its topic category to this. After that
the same for all German blog posts. In Feedburner the feed for "English"
get's used. For all otherr services depending on the language.

 Sample:
http://asmarterplanet.com/blog/category/german/feed = Contains only German
postings (RSS)
http://asmarterplanet.com/blog/category/english/feed = Contains only
English postings (RSS)

 What changes:
Authors will have to assign "english" as a category to their postings (in
addition to the topic category)
The account owner at Feedburner needs to change the source feed to the feed
mentioned above.

 Mit freundlichen Grüßen / Kind regards

 Thorsten Zoerner

 Product Marketing - Content Management and Discovery
IBM Sales & Distribution, Software Sales
ECM IOT NE
  Phone: +49-621469209 IBM Deutschland Home: +49-62016503051 Gottlieb Daimler Str. 12
  Mobile: +49-15112548994 68168 Mannheim E-Mail: thorsten.zoerner@de.ibm.com Germany MyWeb 2.0: Twitter, Blog, Profile IBM Deutschland GmbH / Vorsitzender des Aufsichtsrats: Erich Clementi Geschäftsführung: Martin Jetter (Vorsitzender), Christian Diedrich, Christoph Grandpierre, Matthias Hartmann, Thomas Fell, Michael Diemer Sitz der Gesellschaft: Stuttgart / Registergericht: Amtsgericht Stuttgart, HRB 14562 WEEE-Reg.-Nr. DE 99369940