I can't find a way of controlling the topic title in the mobile output.
I need the very first page to be a "Choose language" option. I have done this by changing the Label of the ToC to "Choose language", after which you get the topics in the .fltoc with top levels of English, German, Spanish et al as entries that don't link to a topic. Further levels in the hierarchy also have entries with no topic. This works nicely in terms of options on the page, but the title bar still says "Choose language" on every page until you get to an actual topic, at which point there is no title at all.
What I want - and expect - is for any particular page that's a sub-ToC to have the title of the "owning" ToC entry.
Does that makes sense?