What is NLS_LANG environmental variable?

NLS_LANG is a client side environmental variable. To specify the locale behavior- setting the NLS_LANG environment parameter is the simplest way.

With the setting of NLS_LANG parameter on client machine it is specified the language, territory and character set used by the client application. As through NLS_LANG parameter, client character set is also specified so oracle has an idea which is the character set for data entered or displayed by a client program as well as Oracle can do (if needed) conversion from the client's character set to the database character set.


On UNIX machine NLS_LANG parameter is an environmental variable and on windows machine this value comes from registry settings.

The parameter NLS_LANG holds the following format.
NLS_LANG=[Language]_[Territory].[clients character set]
The default value of NLS_LANG is AMERICAN_AMERICA.US7ASCII which indicates that
The language is AMERICAN,
the territory is AMERICA, and
the character set is US7ASCII.

The first part of NLS_LANG parameter is language and it is used for Oracle Database messages, sorting, day names, and month names. Each language has a unique name.
The language specifies default values for territory and character set so if language is specified then the other two arguments can be omitted. Language can have the value like AMERICAN, GERMAN, FRENCH, JAPANESE etc. The default value is AMERICAN.

The second part of NLS_LANG parameter is territory and it is used for default date, monetary, and numeric formats. Each territory has a unique name. Territory can have the value like AMERICA, FRANCE, JAPAN, CANADA etc. If the territory is not specified, then the value is derived from the language value.

The third part of NLS_LANG parameter is the client character set. It specifies the character set that is used by the client application. The client character set used for Oracle should be equivalent to the character set supported for the client machine. This character set should also be equivalent to or a subset of the character set used for your database so that every character input through the terminal has a matching character to map to in the database. Example of client character set is US7ASCII, WE8ISO8859P1, WE8DEC, WE8MSWIN1252 etc.

It is important to note that all three parts of NLS_LANG environmental variable/parameter are optional. This means if any of the parts are not specified then default value is used- may be the default value is derived value. You can specify Territory and/or character set without language value; in this case your must include the preceding delimiter -underscore (_) for territory and period (.) for character set. If you don't include the delimiter then the whole value is parsed as a language name.

For example you can only set territory portion by,
NLS_LANG=_FRANCE

You can only set client character set portion by,
NLS_LANG=.WE8MSWIN1252

The three parts of NLS_LANG can be specified in many combination but all of the combination may not work properly. Like,
NLS_LANG = JAPANESE_JAPAN.WE8ISO8859P1

This combination can be will not work properly. Beacuse the specification will try to support Japanese by using a Western European character set but WE8ISO8859P1 character set does not support any Japanese characters.

So if you set your NLS_LANG environmental variable above then you can't store or display Japanese character.

Some logical combination,
NLS_LANG = AMERICAN_AMERICA.WE8MSWIN1252
NLS_LANG = FRENCH_CANADA.WE8ISO8859P1
NLS_LANG = JAPANESE_JAPAN.JA16EUC

In server machine there is no need to set NLS_LANG environmental variable. This variable is only needed for client machine. The character set defined for NLS_LANG environmental variable should be the subset or equal to the database character set so that oracle can aware of each character set and thus can convert client character set correctly. It is also important that character set value of NLS_LANG variable should reflect client machine supported character set so that client machine can display that properly. For example if japanese character set is not installed in client machine but NLS_LANG parameter is set as JAPANESE_JAPAN.JA16EUC then client will not be able to see JAPANESE characters properly.

Important Notes About NLS_LANG Parameter
1)NLS_LANG is used to let Oracle know what character set client's OS is using so that Oracle can do (if needed) conversion from the client's character set to the database characterset.

2)Don't think that NLS_LANG needs to be the same as the database characterset.

3)The characterset defined with the NLS_LANG parameter does not change your client's character set. You cannot change the characterset of your client by using a different NLS_LANG setting. NLS_LANG is used to let Oracle know what characterset you are using on the client side.

4)Don't think that, if you don't set the NLS_LANG on the client it uses the NLS_LANG of the server (which is not true). If you don't set it then default NLS_LANG as described earlier in this post is used.

5)If the NLS_LANG variable match with database character set then oracle will perform no validation on the character set; and thus incorrect NLS_LANG settings may cause to enter garbage data into the database.

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