The problem is that PAL (European) and NTSC (American/Japanese) frame rates differ. Older Latin American dubs were often recorded for broadcast at 23.976 fps or 25 fps. The 1080p Blu-ray versions run at a consistent 24 fps. If you simply slap the old audio onto the new video, the dialogue drifts out of sync within minutes.
Thus, the fan project was born. Dedicated preservationists took the high-quality 1080p Blu-ray rips (often from the Japanese or US releases) and extracted the pristine Latin American audio track from older DVD releases or TV broadcasts. They then painstakingly synced the audio frame-by-frame to the 1080p video. FullMetal Alchemist Brotherhood 1080p Audio Latino
The best releases (often found in community forums or private trackers) note this work in the file name: [Fansub] Fullmetal Alchemist Brotherhood - 01 [1080p Blu-ray x265][LATINO AC3 2.0].mkv The problem is that PAL (European) and NTSC