Thanks for response!
Yes, it happens exactly that way and assigns "tag-ru" to post. So, on output I have post with tag "tag-ru" (without "tag").
In my tags tab (Dashboard) it looks like this:
"estate" -> label "estate"
"estate" -> label "estate-ru"
That posts doesn't have translated versions and I turned off synchronization for taxonomies after the first time this happened.
I'll try default theme without plugins and reply.