@itfs: You might want to ask a moderator to move your post to the
Dictionary FAQ topic where it belongs.
Kindle dictionaries definitely support accented characters, but unlike Mobipocket Reader, Kindles will only display the first match and depending on the dictionary attributes words with accented characters might be treated like words without accented characters or vice versa.
Also you can't look up multiple words with the popup dictionary.
Edit: I found out that it is possible to look up multiple words.