This is the only case I ever hear anyone use the word “internment” so to me “internment camp” is just a synonym for “the place America put Japanese people.”
And “concentration camp” similarly means “the place the Germans put Jewish people (and other groups).”
I don’t think one word is inherently more intense than the other. The difference in how I think about the two is mainly down to what happened in the camps. Both were evil places where the government imprisoned innocent people. Only the Nazis were killing everyone.
Since we are cherry-picking terms, what most people imagine when the term 'nazi concentration camp' is mentioned is actually extermination/death camp. Organized mass murders predominantly via gas chambers or shooting. Wikipedia mentions 6 of those - Chełmno, Belzec, Sobibor, Treblinka, Majdanek and Auschwitz.
Concentration camps per se were just as name suggest - place to concentrate large group of undesirables, either for further sending ie to death camps, or organized hard labor of anything reich required. That horrible things happened en masse and conditions for survival were slim also here was just down to humans (at least in appearance) who ran it.
And “concentration camp” similarly means “the place the Germans put Jewish people (and other groups).”
I don’t think one word is inherently more intense than the other. The difference in how I think about the two is mainly down to what happened in the camps. Both were evil places where the government imprisoned innocent people. Only the Nazis were killing everyone.