Hi Multilang. At a guess, I'd say yours is a travel site? Google seems to rank travel sites differently on local Googles. they seem to give less emphasis to incoming links and more emphasis to the words on your page. I guess this is because they think local sites are likely to have less pagerank than big international sites, and they therefore play down the pagerank effects for travel sites (on local googles) to give local sites a boost.
Rencke - Aren't you worried about the cross-linking penalty? 19 sites all linked to each other sounds high risk to me, even if you aren't doing it to get a pagerank boost. Google might wipe you from the face of the database if they have a bad hair day.
Heini - local domains are not always possible to buy unless you have an operation in that country.