LexiconBase is what the API module communicate with in order to read and edit entries.
LexiconBase communicate with Speechoid to retreive entries not located in local persistency, and push data to Speechoid that has been updated in local persistency.
LexiconLocalPersistency in an abstract storage for updated lexicon entries, probably a strategy pattern of LexiconBase. A setting in extension.json decides on what strategy class to use.
An initial LexiconLocalPersistenecyWANCache could be implemented to get things working quick.
LexiconLocalPersistencyNamespace and LeixconLocalPersistencyWikidata are probable future implementations.