Infinite Health. Get two bottles and a telescope and go to Grandma's. You must fill one bottle with Elixir and set this bottle to Y. After that, press Start + Y and put an empty bottle in Y. Thus you will get one bottle full of Elixir and one bottle half filled with it. Now, you have to set the full Elixir back to Y and press Y + Start. Finally, select the telescope on Y.
Hyrulian language. If you want to understand it, just successfully complete the game.
Change background music. Use Zelda as a name when loading a new game.