Hi.
is there a reason why the payment connector gets locale/localization/language code always from the store, and not from the active user preferences?
If the store has a locale of 'en-us' and the POS user has language code e.g. 'fi', the POS shows all standard labels in en-us, but if your payment connector uses localized strings, the connector locale is 'fi' and all of the payment connector strings are in Finnish.