I have an app that supports English and Arabic. If a German user has Arabic in the languages for their iPhone, the app is switching to Arabic, since that language is one of their languages.
How do I get it to only use the top most language (their most preferred language) they have set? So a German user that does not have English in their languages or maybe has it below Arabic, will still get English as their language
If a user has selected German and Arabic and not English, why do you want to show them English?
My guess is that they have Arabic in their list of languages
Check that. (Ask them to send screenshots of the Settings screen.)
If the user has Arabic specified in their Language & Region settings and it is above English — or if English is not listed — then the behaviour of using Arabic in that case for an app that supports only Arabic and English seems correct. If the user wants to give preference to English, then they can add English to their Language & Region settings and place it above Arabic.