Event Timeline
I do not think design research is necessary since we already have sufficient information this is a desired feature.
Firstly there are multiple use cases where this would be a helpful if not critical feature, as outlined in the user needs evaluation spreadsheet.
One prime example would be for a Health worker traveling to another country wishing to access medical articles in their native language and also in the language of the place where they will be working. This also more broadly for the many existing multilingual Wikipedia users.
Moreover, it's worth noting that there are multiple feature request tickets from users asking for this on Kiwix:
https://sourceforge.net/p/kiwix/feature-requests/985/
https://sourceforge.net/p/kiwix/feature-requests/840/
https://sourceforge.net/p/kiwix/feature-requests/108/
https://sourceforge.net/p/kiwix/feature-requests/574/
https://sourceforge.net/p/kiwix/feature-requests/912/
And it is also requested in Kiwix Play store reviews. There is even a response from the Kiwix team to one such review, where they say "It's true that Kiwix for Android is not able to deal with many files at the same time and this is something we want to fix before the end of the year."