Function 6507h          Get Double-Byte Character Set                DOS 4.0+

    Returns the address of a buffer containing values that specify the
    valid ranges for lead bytes in the given double-byte character set
    (DBCS).

        Entry   AX    = 6507h
                BX    = Code page ID (0FFFFh = current code page)
                CX    = Size of buffer (min. 5)
                DX    = Country code (0FFFFh = current country)
                ES:DI = Pointer to country info buffer

        Return  Buffer updated
                or
                AX = Error code, if CF is set
                     | 01h Invalid function (CX < 5)
                     | 02h File not found

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    Format of country info buffer:
        Offset  Size    Description
        00h     1       Info-ID (= 07h)
        01h     4       32-bit address of DBCS table

    The DBCS values start with a 16-bit value that
    specifies the length of the table. The remainder of the table
    consists of pairs of bytes with each pair specifying the low and
    high character values for a valid range of lead byte values.