Interface to be implemented by an additional dictionary. This can be used to add an expert
dictionary like a medical dictionary or a chemical dictionary.
Gets the list of custom words for this locale. The implementation can decide if there is a
custom dictionary for each available language or only one. This method is called before the
language change event is fired if the language is changed and the dictionary is loaded.
Parameters:
locale - The locale of the selected language.
Returns:
A list of words delimited with line breaks. It can be null.