I noticed that the price of Bitcoin change much like all altcoins.
But the price of other traditional currencies like the euro, for example, are stable and do not change much.
It is the government that control their prices?
Bitcoin is decentralized while the traditional currencies are centralized money. Being decentralized mean, among other things, to not have someone or something that can take care of you. Bitcoin is free to do what "he do". While the centralized currencies are subject of care from the Central Banks (not the governments) of the respective countries which control those and their value controlling mainly the supply of those at the market.