How do we control/tweak the language for the online confirmation message and auto-confirmations?

If I understand correctly, you must be referring to the Custom Thank You Message and the Autoresponder E-mail of the form.

As of now, the multi-language tool does not affect the Thank You Message and the form Email message.

If you need the Thank you message and Auto email message translated, you will have to do it manually on them. That is, you will need to translate them in a static way. It will not dynamically change in accordance to the language the form have when using the multi-language tool.

user guide: -How-to-make-your-forms-multilingual

Hope this help. Please let us know if you need further assistance.

Thanks.