Steps to reproduce:
- With app language set to English, open the English WP article "London"
- Tap the interlanguage button
- Tap the entry titled "Лёнда" in the list (which is lacking an associated language name - probably a related bug)
This should lead to the article "Лёндан " on be-tarask WP, but instead results in a "This page does not exist" error.
The problem is very likely related to the be-tarask/be-x-old inconsistency described in T111853 .