Forum Moderators: open
John Bertrand
If you have a top ranking, just hold your breath and do your evening prayers. Don't change things around beyond what you mentioned. Time works in your favour. Top ranking means lots of clicks, which will be noticed by those engines measuring click-throughs. High ranking also means that lots of people will link to you, at least as long as you offer good content on the topic for which you rank high. More links will push you further up page 1.
As to European keywords, I would guess that all the people frequenting this forum have keyword databases at hand and are willing to part with info from them against a fee. Just sticky-mail anyone who has posted in the discussions specific for the languages you are interested in and ask. Otherwise, you can find sources for mining right here [webmasterworld.com].
The solution of choice is to set up each translated site under its own domain name, containing one or two keywords in the local language, e.g. www.quelquechose.com, www.irgendwas.com etc.
If it is too expensive to translate the entire site, you could set up just a translated index page (e.g. a framset), linking to the rest of the content in English on some other site. This is second best.
If you cannot afford separate domains and need a cheaper solution, then having the other languages on the same site will work, as witnessed by the case story in the discussion I linked to above. This would be your third choice.