De-/Encode MAILBOX Names UTF-7

I need to transform mailbox names (received with IMAP commands) into readable strings.
Mailbox names are using a modified UTF-7 encoding, sadly the commands for encoding/decoding UTF-7 in 4D using Convert to text and convert from text do not work at all!
How can I transform this : “INBOX.Gelöschte Elemente”
into this “INBOX.Gel&APY-schte Elemente” if

$t_Name:=“Gelöschte Elemente”
CONVERT FROM TEXT($t_Name;“UTF-7”;$blob)

does not even work!?
It should return

“INBOX.Gel+APY-schte Elemente”

instead I get

“INBOX.Gel?schte Elemente”

Please advise
Thanks>Product :4D - 4D Server

4D’s CONVERT FROM TEXT/Convert to text offers common/practical encodings that cover most cases.

But if you need to process an encoding that is not supported,
you could consider

https://github.com/miyako/4d-plugin-text-convert

it is a collection of wrappers: