The question was, how would you use this if you have i18n requirements. Format strings are normally part of a translation. I think the bad answer is to embed the entire f-string for a translation as usual, except this can't work because C++ f-strings would need to be compiled. The better answer is, don't use f-strings for this because you don't want translators to monkey around with code and you don't want to compile 50 versions of your code.
Even if you told them, "just copy the names from the original string" it's still asking for trouble, and maybe even security holes if they don't follow instructions. But the biggest problem with the idea is surely that the strings need to be compiled.