unexplainable search problem

i am afraid there is a problem with search when using cyrillic symbols in utf-8: could anybody tell me why a russian word with spaces before and after

?????????? (not sure it will be displayed correctly)  is found, but if there is a point or comma after the word:

??????????.

the search returns nothing?..

in this connection: is it a problem of incorrect set of utf-8 (i only changed encoding in lang/... /common.php) or could it be a problem of sqlite indexes or of the search machine itself ? (and is there detailed instruction on how to switch forum to utf-8?)