Section Translation uses the new language selector (T253303) to let users select a language pair in different situations. For example, the language pair in which to show suggestions, or when starting a new translation.

Currently it is not possible to select as source the current language that is selected as target. For example, if the current language pair is English -> Spanish, the language selector for the source language won't list Spanish as an option even if contents are available for such language:

This ticket proposes to follow a different approach: if the user selects as source the language currently selected as target, respect the user selection for the source and change automatically the target to be the previous source language. For example, in the English -> Spanish example, changing the source to be Spanish would result in the Spanish -> English language pair. This swapping is currently supported in the Content Translation dashboard, but not in the new Section Translation one.

In this way, it is prevented the situation of both source and target being the same language, while exposing the options available and making swapping the languages easier (without additional steps).