Why Hitler choose a swastika as a symbol of Germany during world war 2?

Originally, the Swastika was and still is a sacred symbol in Hinduism and is very common in East Asia and Southeast Asia.

The symbol was adopted, if you will. Or "taken" by several organizations and more importantly, the Nazi Party. It's used to serve as "German Pride". It later became known as a symbol of antisemitism and terror. Because of this, if you travel the world. Different people will give you different perceptions of this symbol. Some will relate it to Hinduism, while many reference The Nazi Party.

Long story short - It was a glorification symbol to Germans, but it relates to a lot of terror and antisemitism.

late nineteenth century, following extensive archaeological work such as that of the famous German archaeologist Heinrich Schliemann. Schliemann discovered the hooked cross on the site of ancient Troy in modern Turkey. He connected it with similar shapes found on pottery in Germany and speculated that it was a "significant religious symbol of our remote ancestors."

However, the work of Schliemann soon was taken up by movements that wanted to evoke racial purity, "Aryan identity" and German nationalist pride.

This belief that the "German race" descended from the Aryan race is likely one of the main reasons the Nazi party formally adopted the swastika or Hakenkreuz (Ger., hooked cross) as its symbol in 1920.