I have an Italian 3DS and I've bought a second-hand English Mystery Dungeon: Explorers of Darkness. I should be able to play it, but I can't, and I don't know why.
According to this question "Can I play DS games from any region on 3DS?":
While all 3DS software is region-locked, Nintendo DS software is not. Because that region-locking isn't encoded into the DS software, you can play software from all regions on your 3DS.
However, software specific to the Nintendo DSi are region-locked, as Wikipedia states.
I thought that maybe that game itself could be region-locked, but the only region-locked Pokemon game should be Pokemon B2W2, according to Serebii:
The games can be played on any model of DS and 3DS, however they contain a region lock on DSi and 3DS models.
I'm pretty sure that Mystery Dungeon is not an enhanced DSi game. As I've found on Gamefaqs:
There is an easy way to tell if a game is DSi-enhanced or not: look at the letters on the bottom of the label on the cartridge. If it begins in "TWL", it's DSi-enhanced. If it begins in "NTR", it isn't.
And that's not the case.
So, here's my question: is there something I'm missing? Why I can't play that game on my Italian 3DS?
Here is a picture of the cart: