I get an error reliably when switching from the mobile website (Esperanto) to the mobile app (Spanish). I believe the mobile app tries to load the last studied language regardless of location. When Esperanto matches nothing/null from available languages a popup list appears asking what I would like to study.

To reproduce the problem: 1. study a beta stage language 2. open the mobile app on Android

By the way I was able to study Esperanto for one glorious lesson on my phone because of this bug.

General recommendation to fix the problem/pseudo-code: if (lastChosenLanguage == null) { // don't try to switch to null before trying available languages: for (int i = 0; i < availableLanguages.length; i++) { if (availableLanguages[i] != null) { currentLanguage = availableLanguage[i]; }}}

Or even easier just use the last chosen mobile app language for the current chosen mobile app language on Android.