LANG operand of the MODEENT macroinstruction

For TSO/VTAM, this operand affects (but does not necessarily decide) the following functions:

The language of certain TSO/VTAM terminal user messages
The language returned on the GTTERM macro
The single-byte character set (SBCS) filter
The device double-byte character set (DBCS) capability

The high-order bit of LANG is used, in conjunction with other LOGMODE information, to determine if a device is queried. A device is queried if it is extended data stream capable and either the high-order bit of LANG (from the MODEENT macroinstruction) is on, or the LOGMODE indicates to query for alternate screen size. The query of the device can affect each of the functions listed above.

Note: The high-order bit of the LANG operand is always obtained from the logon mode table entry (specified by the LOGMODE operand). If the terminal user enters a LOGON command, the LANG or LANGTAB operands of the LOGON command will override the low-order 7 bits specified by the LANG operand of the MODEENT macroinstruction.

The language of TSO/VTAM terminal operator messages IKT00201I through IKT00204I (logon failure messages): TSO/VTAM attempts to retrieve these messages from the MVS™ message service (MMS), so that they can be issued in the language required by the terminal user. The language for all other TSO/VTAM terminal user messages is set (determined) by the PLANG operand of the PROFILE command.
If the device is queried and the high-order bit of LANG is on, the language obtained from the query (if known) is used for the language of the messages.
The language returned on the GTTERM macro: The TSO terminal monitor program (TMP) or command processor may issue the GTTERM macro to determine the language of a TSO/VTAM user. The PROFILE command does not affect the results of the GTTERM macro.
If the device is queried and the high-order bit of LANG is on, the language obtained from the query (if known) is used for the language returned by the GTTERM macro.
The single-byte character set (SBCS) filter: If the device is queried, the appropriate SBCS filter is used (U.S. English filter, Katakana filter, or no filter). If the device is not queried, the SBCS filter is determined from the language value.
TSO/VTAM uses this filter in TPUT data validation and translation. TSO/VTAM performs character filtering for the FULLSCR, EDIT, ASIS, and NOEDIT options of the TPUT and TGET macros.
The DBCS capability of a device: If the query reply indicates that a device is DBCS capable, TSO/VTAM enables mixed DBCS strings to be sent and received from the device. If not queried, the device is assumed incapable of DBCS processing.

If you want to disable the character filtering of TSO/VTAM, code LANG=X'7F' for a device that does not support double-byte capability, and code LANG=X'FF' for a potential double-byte character set (DBCS) device.

If an incorrect LANG operand value is specified or if LANG is not specified at all, the single-byte language defaults to U.S. English.

The low-order 7 bits indicate the single-byte language that is to be used. If a query is issued to determine double-byte capability and the high-order bit of LANG is on, any supported single-byte language value returned in the query reply overrides the value specified on the LANG operand.

The following indicates the bit settings for single-byte languages:

Bit: Description
0... ....: Indicates that the device should not be queried for language information.
1... ....: Indicates that the device should be queried for language information. This value should be used for devices that will potentially process DBCS data.
.nnn nnnn: Indicates the language. For a list of valid values, see z/OS Communications Server: SNA Programming.
.111 1111: Indicates that SBCS filtering is disabled (no SBCS filter). Although not a valid language, this value can be used to disable character filtering. Note that any language other than U.S. English (X'00' or X'01') or Katakana (X'11') will also disable SBCS filtering.