Apps are an international business, but plenty of apps are targeted at one country or region only.

App Store locality

However, by default (iOS) apps are available in all App Stores worldwide. You might consider disabling irrelevant App Stores under Rights and Pricing in iTunes Connect. Just be aware that by doing so, e.g. Dutch emigrants  living in Spain will not be able to download the app anymore.

App locality

More important for your app is setting it’s primary language, which is English by default. If your app has only one language, not being English, then the content and labels in your app will be fine regardless of this setting. However, the primary language does show on your App Store listing as well as being used in any system dialogs, like the in-app Ti.UI.EmailDialog, like shown here:

To change the primary language, set the language_REGION string via your tiapp.xml like shown in this gist: