General

Use the setlocale() call to check which locale is in use, by passing a null pointer as the second argument to query the current locale. For reference, see the man page for setlocale().

If a locale is set up correctly, mblen() will return the correct number of bytes for either a single byte or multibyte character.

Most UNIX terminals support Korean EUC (KS C 5601-1992), and most popular Korean dumb terminal suppliers support Johap (KS C 5601-1992).

Asian characters number in the thousands, so a special input method program is needed. From one to five keystrokes are required to compose one Korean character on the English keyboard, or you can use a Korean keyboard which contains additional compose keys and has a different layout.
Most Korean dumb terminals have their own input method program stored in ROM.
Solaris (dtterm) can convert ASCII character input to Korean characters.

They are displayed as meaningless characters or "garbage".

To produce a compose character in the Latin-1 codeset on x86 systems, press Ctrl Shift F1 to switch to compose mode, and then press the keys that are required for the character. For example, to produce ?, switch to compose mode and then press A ". To produce an inverted question mark (?), switch to compose mode and then press ?. For more information, see /usr/share/lib/keytables

NOTE: The SPARC keyboard uses the Compose key to switch to compose mode.

No. The curses library is not part of libc. The curses man page states that libcurses must be specified as follows:
cc [ flag ...] file ... -|curses [ library ... ]

We can write some simple functions to check whether a string contains some Chinese characters, the following are the C functions to check GB2312 (isgb), GBK (isgb18030_2) and GB18030 (isgb18030_4) characters:

static int isgb(s)
unsigned char *s;
{
    if(s[0] >= 0xA0 && s[0] <= 0xf7 ){
      if(s[1] < 0xA1 ||  s[1] > 0xfe)
        return False;
      else
        return True;
    }else{
        return False;
    }
}

static int isgb18030_2(s)
unsigned char *s;
{
    if(s[0] >= 0x81 && s[0] <= 0xfe ){
      if(s[1] < 0x40 || s[1] == 0x7f || s[1] > 0xfe)
        return False;
      else
        return True;
    }else{
        return False;
    }
}

static int isgb18030_4(s)
unsigned char *s;
{
    if(s[0] >= 0x81 && s[0] <= 0xfe ){
      if(s[1] < 0x30 || s[1] > 0x39)
        return False;
      else
        return True;
    }else{
        return False;
    }
}

The alternative key for the Compose key is Control+T, i.e., pressing Control, Shift and t keys all together, and it will work for any keyboard.
There are certain AltGraph key related compose sequences, particularly, euro sign, and in recent Solaris Unicode locales and some Linux systems support additional compose sequences such as, well, either or both of the following:

	Compose c =
	Compose e =