Safari supports base64-embedding font files in a <style>’s @font-face {} (iirc it's something like `@font-face { src: url('data:application/x-font-woff;charset=utf-8;base64,...'); }`) that can then be referenced as normal throughout the SVG. I don't recommend this though, nobody wants to deal with 500KB SVGs.
You can also point to font files with @font-face. I use a small custom font that's only 16 KB. Although, when opening the file locally, you have to first disable local file restrictions in safari's settings before it works...