bytesToString or convertToValues (passing an InputStream or a byte array–not a string) and specifying the correct encoding used in the bytes is indeed a good way to convert.
Possible character encodings for Cyrillic listed at [URL]JDK 19 Documentation - Home
ISO8859_5 - Latin/Cyrillic alphabet
Cp1251 - Windows Cyrillic
Cp855 - IBM Cyrillic
Cp1025 - IBM Multilingual Cyrillic: Bulgaria, Bosnia, Herzegovinia, Macedonia (FYR)
There are others. The key is to get the encoding/code page being used by MVS from your Russian colleagues.
I’m not sure if the conversion to/from EBCDIC will be handled by this but hopefully this is enough to get you on the right path.
#Integration-Server-and-ESB#webMethods#webmethods-Protocol-and-Transport