A local Playlist file (such as an M3U file) is simply a bunch of text lines which describe the precise folder details and filename of each audio file on your device's local storage. There is no information about the content of the file, just the exact filename. If the exported data from Spotify (such as a CSV file) can be manipulated to create a match for your local filename structure, it could work. From a Google search, an example CSV export of three songs from Spotify might look like: