Localized banks are functionally treated as the same bank by the API, despite the difference in file name. This means that localized banks loaded after the first aren’t loaded or registered with the Studio System, and that Studio.System.getBankList() only returns the non-localized bank name (i.e. “Dialogue” instead of “Dialogue_EN”).
Since you’re using FMOD for Unity, you can use RuntimeManager.HasBankLoaded() to query the banks that have been registered with RuntimeManager. If you’re not making use of RuntimeManager, you’ll need to track this information yourself in order to query it.