Generally speaking, racial slurs are pretty stable. If someone takes an issue with blacks, or Jews, or Japanese, or Italians, or Irish, or White Anglo Saxon Protestants, we know what terms they would use today, which is what they would have used 100 years ago. But I am not aware of the term "Huns" being used against the Germans after WW1. Why is this?
I'm not sure I see the premise of the question.
British poster:
https://commons.wikimedia.org/wiki/File:He_Needs_Our_Ammo%27_to_Shoot_Down_Huns_Art.IWMPST14411.jpg
American poster:
Sometimes the language of propaganda posters is slightly removed from the quotidian, but it would seem strange for 1940s posters to be using language that was obsolete.
Contemporary caption on 1941 operational photographs:
https://ibccdigitalarchive.lincoln.ac.uk/omeka/files/original/1380/24022/PFordTA17040018.1.jpg
It's regularly used in Clostermann's "The Big Show", at least in its (1950s) English translation (I have a 1951 edition to hand). p.76 "Either on the one hand the Hun was trying to bluff us". p.170 "The few Tempests and Hurricanes which managed to intervene shot down 36 Huns". That shows it was regular use in 1951, if not 1944-5.
My copy of Don Bennett's memoirs is not immediately available, but it is quoted here:
"They told the Hun we were coming to Berlin every night without exception".
