4.4.3 Language conventions of user-created plug-ins
If you pass lang (language information) to a method of a user-created plug-in, the language setting of the WWW browser is passed to it when you execute the method from the window of JP1/IM, and the value specified in the Accept-Language header of the HTTP request is passed to it when you execute the method from a REST API.
Make the user-created plug-ins work in Japanese mode when ja or ja-JP is specified or in English mode if en is specified.
Define how each plug-in works if a value other than these values is specified. If lang is omitted or any undefined value is specified, make the plug-ins work as if en is specified.