In case anybody tries to do this with flakes:
final: prev: {
mdbook-multilang = prev.mdbook.overrideAttrs (oldAttrs: rec {
pname = "mdbook";
version = "pr1306";
src = prev.fetchFromGitHub {
owner = "Ruin0x11";
repo = "mdBook";
rev = "9d8147c52dd9d50047ba5b29e4af99f92577806e";
sha256 = "sha256-gJnQKHssO2ChiT4d037Lncd7hiOa5uh756p8TzPzbgQ=";
};
cargoDeps = oldAttrs.cargoDeps.overrideAttrs (prev.lib.const {
name = "${pname}-vendor.tar.gz";
inherit src;
outputHash = "sha256-QCEyl5FZqECYYb5eRm8mn+R6owt+CLQwCq/AMMPygE0=";
});
});
}