As you might have guessed, Shelves relies on The Internet to populate information about all of the items it manages. It asks a database whether or not an item exists, and if it does, pulls that information down. To put it simply, unless there's a source online that's willing to provide information about an item, it's impossible for the app to fetch it.
Similarly, different sources provide different pieces of information. For example, the source that provides information about board games does not provide information on barcodes for those games; thus, there's no capability to use the scanner whatsoever. Other item types offer more information, and so Shelves works around that content to provide a rich user experience.
The same is true for region support. Shelves can only acquire regional information if a source for that region exists. It's not a matter of preference or prejudice; it's all about finding a reliable source online that provides specific product information about a region. At the moment, only items from the following regions are supported:
If you know of a region or item that can be supported, by all means, contact me and I'll try to add it!