I tried to purchase an app from Windows 8 app store. I can neither use my PayPal account nor my Visa card as it requires a United States address.
If you're currently living outside the US and have your Home location in Windows' Region settings set to United States, it allows you to use English version of Microsoft Store, read reviews in English, etc.
However, this setting will prevent you from using your credit card issued outside the US for making purchases in the Microsoft Store. If you set a different country as your home location, this allows you to purchase apps using your non-US credit card, but it also ties you to the non-US part of the Microsoft store.
Please keep in mind this might prevent you from finding or installing apps if they are not present on the current version of the Microsoft Store due to geographical restrictions, specially if you buy an app in one store and then change to another version.
Source: MS Technet
Related: See the list of countries or regions where the Windows Store accepts payment in the local currency (MSDN).