Converting mailboxes to UTF-8

Is any proven routine to migrate mailboxes from mUTF-7 to UTF-8 encoding?

I've try to use doveadm list/mutf7/rename but have been stuck with nested inboxes. Say I have the next structure:

INBOX INBOX.жыр INBOX.жыр.ядъ

encoded for FS respectively as

.INBOX .INBOX.&BDYESwRA- .INBOX.&BDYESwRA-.&BE8ENARK-

​When I've try to rename ​INBOX.жыр with

doveadm mailbox rename -u me -s "INBOX.&BDYESwRA-" $(doveadm mailbox mutf7 -7 "INBOX.&BDYESwRA-")

I've get the next:

.INBOX .INBOX.жыр .INBOX.жыр.&BE8ENARK-

​Sure when I've try to rename ​.INBOX.жыр.&BE8ENARK- I've get a message that this is not a valid mUTF7-encoded string.

So that is the question.