Include user's language in body of outgoing slash command request
Currently, outgoing Slash commands send in the request body information about the user like userid and username.
However, to properly internationalize a slash command integration (such as https://github.com/jedfonner/MattermostOnFire/issues/2), the receiving system needs to know the user's specified language (from Account Settings > Display > Language).
Please add a "user_language" field to the JSON object passed in the body of the message sent by Mattermost outgoing slash commands. This field should be populated by the user's language (e.g., en-US, es-MX, fr-CA, etc).