Doesn't have to be a DB problem ... (though could well be)... an example:
I imported a UTF8 encoded table with 3rd party data into my CMS. I got encoding problems on the front-end as the script I used to access the DB was improperly encoded.
Here are some common sources of conflict I encountered with encoding:
1) Own scripts improperly encoding
2) Core files modified with editor not set th UTF8 (changed files were saved in wrong encoding)
3) On DB roll-back encoding for import was improperly set (mySQL was not explicitly set to utf8)
4) Encoding settings not stated in template
5) Wrong use of uf8_encode and utf8_decode in PHP
Probably these can help you to nail down the problem
What does your DB say? What encoding is it using?
I use the string "Iñtërnâtiônàližætiøn" to check for proper encoding. What happens with this string in regular content?
Best
Nils
edit:
however, the string mentioned above only covers Latin-1 range... if you want to check for double byte character-support, check this string "Ādam", the first character is U+0100 (or copy paste some Kanji from Google Japan).
not a real solution I know... but may be helpful for future testing.