The English sentence doesn't make sense to me.
The French translations doesn't match (years - jours, been dead - cru mort)
And I think the German translation of this sentence would be "Er war drei Jahre lang tot" ?

A more literal translation of the Japanese would be
"It's been three years since he died."

There is nothing wrong with the original English sentence, and the Japanese is probably the closest to the English that you can get.

Your German suggestion "Er war drei Jahre lang tot" would be a translation of "He was dead for three years", which also implies that he has somehow come back to life now.

ok, thanks, I thought, there was a difference between "for three years" and "since three years".
apparently the French translator had the same problem as I did, so if someone corrects the French version, the rest should match.

thank you for your explanation, wolf, I read your comment only now. now I understand.

Ok, I corrected the French version.