Internationalization and localization allow applications to be used by people in different languages and using different written contexts (e.g., date formats). Conceptually simple, it’s a powerful way to make software available to more people.
As a native English speaker in a predominantly English-speaking country, I think it’s fair to say that most native English speakers in English-speaking countries give little thought to how their software will be used by people who speak other languages or by those in other countries. However, writing software for only one language “market” works against your ...