Playing local multiplayer between US and EU models

If it doesn't work, change the region.

 

Afaik no.

Sorry. I wanted to write: "If nothing works".

 

[Release] Dead Simple EULA Set

 

That allows playing online for out-of-region games by accepting user agreement for that specific region or country. I do not know if it applies for Download Play or local play.

Some games won't play together if you and a friend don't have the same exact game (ie, different TitleID or from different region). One of you would either have to dump and share their copy of his/her game or go & download it from Internet.

• Dumping d’un titre (Dumping a Title)
• Convertir un .3ds en .CIA (Converting a .3DS to .CIA)
• 3dsdb.com
  
• [hax0kartik.github.io] 3dsdb

 

Apply the EULA agreements on both the USA o3DS and EUR n3DS with that DSES homebrew app. That'll should allow the USA o3DS to participate in online games in the EUR only server, and EUR n3DS to do the same on the USA only server.

Also, you might need to create or link a NNID, Mii character, and add the two systems to one another's Friend List before they can find and play together.

 

I don't think you can play together locally through Download Play. Let's say one of the 3DS systems has a NES Virtual Console game, and you want to do a two players gaming session. When the 3DS with the game goes to host the game in Download Play, the other 3DS won't recognize the announcement because its Download Play only works with those of the same firmware region.

• Download Play (USA) - TitleID: 0004001000021100
  
• Download Play (EUR) - TitleID: 0004001000022100

You can try to dump the system title CIA of the EUR version of Download Play like this.

• Dumping d’un titre (Dumping a Title)

1. From the EUR n3DS using GodMode9, [1:] SYSNAND CTRNAND/title/00040010/00022100/content/0000000#.tmd → TMD file options... → Build CIA (legit).
2. Copy the sdmc:/gm9/out/0004001000022100 Download Play (CTR-N-HDLP)(E).legit.cia to the SD card of the USA o3DS.
   
3. On the USA o3DS, backup the SysNAND *.bin image for safety.
   • Création d’une sauvegarde de la NAND (Creating a NAND Backup)
4. FBI install the CIA of the Download Play (EUR) on the USA o3DS.

If successful, you should be able to launch that copy and connect to the EUR n3DS.

If you manage to softbrick the 3DS firmware due to later deleting the wrong system titles or the installation goes wrong, restore the SysNAND with the image made in step 3.

• Restauration de la sauvegarde de la NAND (Restoring a NAND Backup)