Thank you Claude31 for your detailed explanation.
You let my understand that the error in my simple example (from "Streamline your localised strings" in WWDC21) is the use of %d, which refers to 32bit integer, instead of %ld, which refers to 64bit integer.
While I corrected the mistake, I realised that a widely portable stringsdict should have all theoretically possible values, i.e. "Order %d" (int, or 32-bit integer), "Order %ld" (long int) and "Order %lld" (long long int).