The Google Play Store as it stands today, is available in the vast majority of countries around the world. But there are still quite a few countries that Google's Play Store is not available in. Of course, the most well-known of those countries is China, and that's due to the country actually banning everything that Google has. Now it looks like the Play Store may soon be arriving in China, Cuba, Iran, Macau, Myanmar and Sudan. These countries all showed up in the Google Play Developer Console area, where developers would be able to make their app available to users in those countries. Meaning that a Google Play Store launch is pretty imminent.
For China, the Google Play Store notes that in-app purchases are not available because users are not able to purchase through the Google Play Store in that country. This could be one of the many things that gets taken out of the Chinese Google Play Store when it launches. It has been rumored to have been preparing to launch for a couple of years now. The search giant was supposedly working with the Chinese government on a censored version of the Google Play Store so it could come back to China. But so far nothing has become official just yet. But Google may have waited to long to re-enter the Chinese market. Seeing as with Google out of the market, many other app stores have popped up, making it increasingly difficult for Google to come back and gain a foothold there.
While the Google Play Store has been available in some of these countries already - as noted by several users on reddit - Google has opened up in-app purchases and paid apps for some of these countries. Like Macau and Iran. Which is also a big deal, as it allows developers to start selling their apps and games in those new countries and still make some money from them, which is definitely important for any developer these days. There's no official word from Google just yet on this, but that should be coming soon, or when everything is worked out on their end.