If you still have access to the original source in the filesystem you could just re-read the snippet and recover the original escaped form. If your language off

If you still have access to the original source in the filesystem you could just re-read the snippet and recover the original escaped form. If your language offers only a single way to escape characters then you may even just re-escape the string when emitting the error (although most languages have some sort of codepoint escape sequence)