Returns the extension (or private use) value associated with the specified key, or null if there is no extension associated with the key. To be well-formed, the key must be one of [0-9A-Za-z]. Keys are case-insensitive, so for example 'z' and 'Z' represent the same extension.

Parameters:

key

the extension key

Returns:  The extension, or null if this locale defines no extension for the specified key.

Exceptions:

IllegalArgumentException

if key is not well-formed

See also:
PRIVATE_USE_EXTENSION, UNICODE_LOCALE_EXTENSION

Since:  1.7