In the English language world, does the word "sinned" in that verse also mean an act against God's will or something else?
As an English bible reader we can define sin as follows,
1 john 3:4 nkjv
4 Whoever commits sin also commits lawlessness, and sin is lawlessness.
So in that sense, sin is breaking God's commandment.
However, the idea that babies are without sin before a certain age (you mentioned 3) is debatable.
Behold, I was brought forth in iniquity,
And in sin my mother conceived me.
Here King David is writing a psalm about his specific sins with Bathseba and Uriah. However he mentions that even before this he was born in Sin, Even at his conception (beginning of life) He was made in sin.
As humans, we are not just responsible for our own personal sins, but we are also under the penalty of Adam's sin.
Adam is like the representative for humanity. Imagine the President of the United States attacked Russia and there was now a war between Russia and the U.S.
Im a U.S. citizen, i didnt do anything to attack Russia, but because of what my representative did, Russia still considers me an enemy.
Adam is like our President in that sense, and he sinned against war, causing hostility between humanity and God.
In the English language world, what does the word "death" mean in that verse? Does it mean that the person is not breathing anymore, or that they are spiritually dead?
in English we dont have two different words for "dead" and "spiritually dead."
But the fact is that the two are very related, it is because of sin that we die spiritually, and Physically.
God's original plan for people was that they would live eternally. Physical death is a result of the Spiritual death brought by Sin.
So in that sense Sin causes both "deaths", and the only difference is time (physically death takes ~80 years, which is short when you think of eternity)