How to find out whether a game is region locked or not?

To switch back to your home country store, add /?cc=XX to the url, replacing XX with your country's two-letter code. (US, UK, FR, DE, SE, BR, etc)

As with any rule, there are certain exceptions to this particular method. Dishonored, for instance, is region-locked, despite not having the aforementioned flags in the database - the lock is applied by providing a separate AppID for the Russian version of the game. Any DLC you buy from your own store won't be compatible with the Russian version of the game, and vice versa - this caused headache for a whole bunch of people in the past. Always pay attention to the title of the package you are viewing in the database (Dishonored RHCP (RU) in our case indicates that this is a special version for Russia, Hungary, Czech Republic and Poland).

But exceptions like this are few and far between.

Thanks a lot!