I'm a native German speaker and i don't know of a dialect in Germany that would pronounce "Widerstand" with a short "i". Would you mind sharing which dialect you think of?
"ie" is always long. For "i" it depends on the splitting of the word, i think. I don't know if this is a concept in other languages too. I think the rule is that if the "i" is at a split, then it is long, but i'm not sure and there are always exceptions to every rule in German. Consider "Schnit|zel", "Lis|te" (short) vs "Bi|bel", "Wi|der|stand" (long).
"ie" is always long. For "i" it depends on the splitting of the word, i think. I don't know if this is a concept in other languages too. I think the rule is that if the "i" is at a split, then it is long, but i'm not sure and there are always exceptions to every rule in German. Consider "Schnit|zel", "Lis|te" (short) vs "Bi|bel", "Wi|der|stand" (long).