That depends upon which nation one's from. The UK has used «dice» as both singular and plural for decades. The US generally uses «die» as singular, but the UK use is creeping in as RPGs and boardgames globalize.The English plural of "die" is "dice." "Dice" is already plural.
Interesting. I didn't know that. Is the phrase "the die is cast" not used in the UK?
Here is the U.S., I have noticed that younger gamers are starting to use the plural "dices," which makes my skin crawl.