[Koha] koha sorting issues

Dear list, I have previously written to the list about our issues with sorting search results in our non-latin character catalog. I have been advised to modify the sort-string-utf.chr file but it did not work. Now i am trying to achieve this by converting the character set and collation of the MySQL tables. We have converted the collation of the table biblio, deleted the zebra index and re-indexed it, but still the non-latin character search results are sorted incorrectly, when I sort them for example by title. Could you please advise me which specific table should be altered? In what table is the MARC information stored? Of course, any other advice to solve the sorting issue is also welcomed. Regards, Hayk.