You cannot open just "Part 1" on its own. You must have all parts (e.g., part1, part2, part3, etc.) in the same folder. When you extract "part1" using a tool like WinRAR or 7-Zip , the software automatically pulls data from the other parts to recreate the full .xci game file.
This version is labeled (Asia) . While the Switch is region-free, different regional releases sometimes have specific language packs. Most major Sonic titles include English, but you can verify the supported languages in the emulator settings once it is loaded. Are you having trouble extracting the files, or Sonic Frontiers (XCI)(Asia).part1.rar
The file name indicates that this is the first part of a multi-part compressed archive. To use this file, you generally need to keep the following in mind: You cannot open just "Part 1" on its own