Actually it was a bloodbath.
Some info
here
Some info from there
"More US Marines earned the Medal of Honor on Iwo Jima than in any other battle in US History.
In 36 days of fighting there were 25,851 US casualties (1 in 3 were killed or wounded).
Of these, 6,825 American boys were killed. Virtually all 22,000 Japanese perished."
I think the reason for the captioning is for some reason recent directors feel that this gives a movie a greater sense of "realism". Maybe he thought that since this is from the Japanese point of view, that they should show them speaking their own language.