I'm trying to wite some extension in C.
It's is intended for reading/writing id3 tags from MP3 files.
But problem has raised while developing.

How can i return (for ex) Cyrillic string to TCL interpreter to be shown OK.
In C code I have char* filled with my Cyrillic words.

But when i set result of command with 

Tcl_SetObjResult(interp, Tcl_NewStringObj(buf, -1));

unknown symbols are shown instead of correct word.

[Lars H]: This mostly sounds like an [encoding] problem. 
Check out http://www.tcl.tk/man/tcl8.4/TclLib/Encoding.htm.
You'll probably want to use Tcl_ExternalToUtfDString and then 
Tcl_DStringResult.