Alas, you're really off in the weeds here.
+[NSLocale currentLocale]
returns the current
locale, that is, the value set by Settings > General > Language & Region > Region Formats. It has nothing to do with the language that your app is running in. It's perfectly reasonable, and in fact quite common, for users in the field to have their locale and language set to 'conflicting' values. For example, a native English speaker living in France would have the language set to English but might choose to set the locale to French (so they get metric weights and measures, 24 time, and so on).
The language that your app runs in is determined by the language setting, that is, Settings > General > Language & Region > Preferred Language Order. When the system runs your app it takes this list of languages (the preferred list) and matches it against the list of languages that your app is localised into (the app list). The first language in the preferred list that exists in the app list is the language chosen for the app. This is what you'll find in the first entry of the main bundle's
preferredLocalizations
array.
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