We currently have two ways to buy a game on foreign stores :
You can buy on any store with a VPN.
If this technique is the most effective, it still remains the most complicated.
The other technique is to first buy Xbox Live gift cards, and then use them to buy games on foreign stores.
This technique is the simplest, but unfortunately some stores (Colombia, Argentina, etc) doesn't offer gift cards.
Very interesting technique for stores do not offer a gift card like stores Indian, Colombian, Argentina and Hungarian ! (Thank you for this tutorial Flow791 )
For this, you need an account "Revolut" or "Number26" (optional) and a "VPN".
This step is optional, you can very well pay with your credit card number directly , but if it doesn't work you can try with Revolut and Number26
Revolut, is an application that allows like Paypal have an online account except with Revolut you can order a real card linked to your account Revolut. This is of course free.
Go on Revolut website
Number26 offers the same thing except that's also has a website + app.
Go on Number26 website
For this I suggest you GoldenFrog VyprVPN for all the countries in which stores are interesting because this technique works on all stores. With this one you have 500MB / month free which is more than enough.
Go on GoldenFrog VyprVPN website
Gift cards are zoned.
If you want to buy a game on such Canadian store, you must purchase a gift card in Canadian dollars (CAD). (Do not confuse with American dollars : USD !)
The most reliable site to buy a gift card Xbox Live is Microsoft's official website.
Example for Canadian 100$ gift card.
Warning ! Some gift cards sold on the official Microsoft site are not digital, and therefore are not sent by e-mail but by postal address.
This is the case of Hong Kong gift cards (HK$), if you buy one on this site, the gift card will be sent to a Hong Kong address. So in the end, you will never received it.
Here is a page listing all websites that sell digital gift cards : Where buy Xbox Live gift cards
What you should know is that your wallet are specific to each store (country).
If you credit 100 Canadian dollars to your account. You can't buy games on a store other than Canada with the $100 CAD.
To fund your account, simply go on the "Redeem Code" page on Xbox.com
Left in the menu, click on "My region" and select the corresponding region in the gift card you want to be credited.
Register your gift card, validate, and it's good your account is now credited !
Now that your account has sufficient funds to buy the desired game.
Access the game's page on our site Xbox-Store-Checker, then click on the price in the column "Conversion".
You'll be redirected to the official website Xbox.com with the page of the game, and the desired store.
You have just to buy your game with your Xbox Live balance.
Once purchased, your game will be available directly on your console in the language of your country.