is possible to know the region of the boxed games?

You can use rating icons:
https://www.kaspersky.com/blog/gaming-age-ratings/11647/

Check the listings for the game through SteamDB. It won't necessarily tell you what the region of your copy is, but it'll at least tell you what region-lock variations the game does and doesn't have. If you're in one of the listed regions for a region-locked variant of the game, then it's best to assume that your copy falls under that restriction setting. If you don't see any restrictions for the region the game copy is from, then theoretically you'd be safe in assuming it's a ROW or WW key.

As far as determining the region of the boxed copy where such is unknown and the box doesn't make it clear, I'd imagine your best bet'd likely be to check for any in-box inserts. If you can't determine the region, probably best to just assume that any region using the language on the box would need to be checked against region restriction listings.