Would you mind explaining WHERE to find these controls?
Would it be too much to ask the undoubtedly overworked tech writers to include such info in the actual help docs instead of hoping that a third-party will do the explaining?
It is in the help, the issue is with finding it!
Click Help > Contents & Index.
When the help opens enter Default Language. The important bit is to tick This Reference Only so that you stay in the help. That tells you how to set the default language but not how to get to the screen where you do that. To get to that you need to go up a level, use the breadcrumbs.
I realise it's too late for what you wanted but it may help knowing how to get another answer in the future.
See www.grainge.org for RoboHelp and Authoring tips