After sending the USSD code, I will get a reply in Chinese. Should be Polish.
Problem with software or telephony operator?
Modem manager GUI 0.0.18
This is problem with Modem Manager plugin for Huawei modems. Modem Manager decodes UCS2 answer with GSM7 decoder and sends result to MMGUI that cannot correctly recover source answer. There are two ways to fix it:
1. Easy: tell operator to send transliterated USSD answers and disable reencoding functionality in MMGUI (USSD - Edit - Change message encoding).
2. Hard: prepare patch for Modem Manager and and convince it's developers to accept it.