In a system with multiple languages, A, B, C, D, where language A is the Default and the language order has been set to A, B, C, D
If a user selects their language as B. When viewing lists of content or content items - IF language B is available, the content from language B will be shown to that user
Any content in which language B is not available should be shown in the default language, A
If content exists where the user's selected language (B), and the default language (A) are not available - the system should check the content and display whichever language the content is available in. If for example, a piece of content was available in only languages C and D, the content would be shown to this user in language C because the language order is B (the user's selected language), A (the default language), then C then D
If a user selects the default language as their language (A) then the system would check for language A on content, and if not found would show B (if available) as this is the next language in the language order
So the overriding order to show content in is;
User selected language
System default language
Then whichever is first in the language order
.