[Lazarus] Case error with cirilyc

[theo]

You should not replace multiple characters with this method like

s.Replace('ввв');

It works for me, if I write
s.Replace('в');

It outputs: kввgd then

Make sure your file encoding is UTF-8 (standard)

If you really need to replace with ввв then write the output in a second 
string like you did before.