The request message for [EntityTypes.ListEntityTypes][google.cloud.dia
logflow.v2beta1.EntityTypes.ListEntityTypes].
Optional. The language used to access language-specific data.
If not specified, the agent’s default language is used. For
more information, see Multilingual intent and entity data
<https://cloud.google.com/dialogflow/docs/agents-
multilingual#intent-entity>__.
Optional. The next_page_token value returned from a previous
list request.