Chat Messaging: Conversation bot does not support multiple language for authenticated login user

Dear Support Team,

At the moment, I can integrate conversation bot for Chat Messaging. My conversation bot had configure to support auto translation (same the the post) and I enabled this bot for my chat messaging. 
And when installing the web widget for messaging (as the post) and I use the API core to set the locale to de, with my browser language as English, the chat messaging is shown in German (is expected behaviour). 
But when I enable authentication as the document, the conversation bot is shown in English. And I cannot find the way to configure the language for the conversation bot.
I think that would be helpful to configure the language for conversation bot instead using the browser language.

Thank you,
Hoa