get
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.
Return
The extension, or null if this locale defines no extension for the specified key.
Parameters
key
the extension key
Throws
if key is not well-formed