You can directly read SMS with AT commands on HEX way.
RouterOS do not support at all any special characters of any language.

I even can not to use LTE at all and pull a wire directly to my home, yes, I got it.

And what characters you expect instead of "?" ? Minimum: /tool sms inbox print proplist=message should have option to print message as kind of hex sequence, like json-escaped string with characrters encoded in way \u0012 Maximum: if router receives SMS with UCS-2 chars (e.g. "Ελληνικ...

FR: SMS Support reading UCS-2 messages. At least not break unknown characters to "???" symbols.