When looking for a Monster Hunter 4G 3DS JPN repack, the installation process usually follows these steps: Ensure your 3DS is running the latest Luma3DS CFW.
If the repack includes a translation, enable "Game Patching" in your Luma3DS configuration menu (hold Select while booting). Performance on Old 3DS vs. New 3DS monster hunter 4g 3ds jpn update cia repack