So I was having a similar problem with a multilingual form (3 languages) where ODK Collect crashes, but only when trying to switch to the non-default language that contains extra media (images and/or audio) in questions that don't have media in the default language. I was still able to switch between the 2 languages that didn't contain (extra) media that were not in the default language.
My simple workaround was to change the default language in my XLSForm settings tab to the language that contains the extra media. This has created some interesting behavior in ODK Collect. I'm able to change between all three languages without crashing, however, now those images and audio are displayed for all languages.
For a bit of background in my use case, I'm creating a form to be used by enumerators that are illiterate and mostly monolingual in a local language, as well as those who can read French or English. Keeping things as simple as possible for the illiterate monolingual people is very important. I used Enketo and avoided ODK Collect entirely for a couple of years because ODK Collect's interface introduces too much complexity and is very text heavy, which intimidates/confuses illiterate users.
Ideally, I'd be able to display the French and English without the audio/images from the 3rd minority language, but it is currently not a dealbreaker.