Decrypting is one thing, re-signing is another. We can decrypt save files, however, the 3DS is required for re-signing and only the Cyber Save Editor dongle offers this service for Japanese Cartridges.
3DS encryption (for 6.0+ firmware games) uses parts of the ROM data, and the necessary part for encryption differs between Japanese/International copies, and even for different version revisions (which is why prepatched games have had problems with Cyber Save Editor support).