I'm not even going to pretend that I'm into Indiana Jones. I played the shit out of the Young Indy NES game when I was a snotty kid and read and seen Temple of Doom but I was never a fan of the franchise and know little about it. I actually liked its rip-offs (like Firewalker and Allan Quatermain, even John Rhys-Davies plays parts in these) more. But this gave me an idea:
A ruthless Leibstandarte SS officer from Hitler's personal bodyguard unit played by a de-aged Mikkelsen obtains the Spear of Destiny (or some other Biblical relic) during the time of the post-war Werwolf insurgency after his unit successfully ambushed and slaughtered a group of Allied soldiers. After being on the run for a while he simply enlists in the French Foreign Legion to fight in the First Indochina War like many East Prussian refugees, drifters, orphaned teenage boys and his former brothers-in-arms who became French POWs did. He manages to smuggle the Spear to Indochina with him somehow. He fights the Viet Minh in a brutal fashion but changes sides (1400 of these German legionnaires deserted or switched sides during the conflict) when the tide of war turns. He becomes a staunch Communist like Austrian Ernst Frey and Germans Rudy Schröder and Erwin Borchers who were political exiles and joined the Legion in 1940 to fight Nazis but ended up in French Indochina and chose to side with the Viet Minh under the names Nguyen Dan, Le Duc Nhan and Chien Si in the late 1940s and early 1950s.
Fast forward to 1969. Indy is looking for the Spear of Destiny in Vietnam and bumps into his son who is now a battle-hardened Marine involved in the Combined Action Program and is helping locals defend a mountain hamlet from the Viet Cong. Mutt goes AWOL after a while to help his father find the Spear which is located in some ruined mountain temple. They face a tiger, Charlies, snakes, napalm, booby traps, whatever. Mikkelsen's character is now a high-ranking officer in the North Vietnamese Army and is also in the area. He hears from a VC spy or a captured and tortured American soldier that someone is after the relic. Let the confrontation begin!
Voila! Leftists get their evil Nazis, right-wingers get their evil Communists and I fixed the basic plot of your movie. Fellow Kiwis! Feel free to add more!