10.2. Setting the Error Message Language

By default, mysqld produces error messages in English, but they can also be displayed in any of several other languages: Czech, Danish, Dutch, Estonian, French, German, Greek, Hungarian, Italian, Japanese, Korean, Norwegian, Norwegian-ny, Polish, Portuguese, Romanian, Russian, Slovak, Spanish, or Swedish.

You can select which language the server uses for error messages using the instructions in this section.

In MySQL 5.7, the server searches for the error message file in two locations:

It tries to find the file in a directory constructed from two system variable values, lc_messages_dir and lc_messages, with the latter converted to a language name. Suppose that you start the server using this command:
```
shell> mysqld
                    --lc_messages_dir=/usr/share/mysql --lc_messages=fr_FR
```
In this case, mysqld maps the locale fr_FR to the language french and looks for the error file in the /usr/share/mysql/french directory.
If the message file cannot be found in the directory constructed as just described, the server ignores the lc_messages value and uses only the lc_messages_dir value as the location in which to look.

The lc_messages_dir system variable has only a global value and is read only. lc_messages has global and session values and can be modified at runtime, so the error message language can be changed while the server is running, and individual clients each can have a different error message language by changing their session lc_messages value to a different locale name. For example, if the server is using the fr_FR locale for error messages, a client can execute this statement to receive error messages in English:

mysql> SET lc_messages =
        'en_US';

By default, the language files are located in the share/mysql/LANGUAGE directory under the MySQL base directory.

For information about changing the character set for error messages (rather than the language), see Section 10.1.6, "Character Set for Error Messages".

You can change the content of the error messages produced by the server using the instructions in the MySQL Internals manual, available at MySQL Internals: Error Messages. If you do change the content of error messages, remember to repeat your changes after each upgrade to a newer version of MySQL.