Q:

"en" vs "en-US" as default language for Windows 10 UWP (distributed worldwide)

I'm wondering what could be not obvious consequences from the user experience perspective if I'll choose to go with default language for UWP application as "en" instead of "en-US" and provide localized resources only for "en" culture, but not for "en-US".
Considering that there is not much text in the app I'm assuming that it should behave in English for, say, US-based users and Great Britain-based with equal experience, but just in case would like to be sure about that.
As far as I know if you leave the default language as "en-US" and provide resources for it the app will fallback to it for, say, "en-GB users", so that's where this question arose - what are the pros and cons to go with "en" or "en-US" for application, that is distributed worldwide?
Any thoughts?

A:

As far as you do not differentiate en languages, there shouldn't be a difference if you choose en-US, en or en-*. As MSDN says:

Windows prioritizes matching of languages in a standard well-understood way. For example, en-US matches, in priority order, en-US, en, en-GB, and so forth.
• Windows does cross regional matching. For example, en-US matches en-US, then en, and then en-*.

Providing en-US and en would make sense if for example you have resources specific only for US, and other resources for the rest of en languages. 

