Using temporary variables or calling a method directly
Regarding speed and memory, both are completely equivalent.

The only thing this boils down to is readability. In which case the first option has an advantage.

By storing the Button button = (Button) findViewById(R.id.button_english_splash); in a temporary variable, you have the opportunity to give it a good variable name, in case the R.id identifier is not good enough.

Also, method calls like ((Button) findViewById(R.id.button_english_splash)).someMethod are often not very readable as there are several parenthesis that are added.

I would recommend sticking to the first option. Perhaps not always, but mostly.

Other comments:


Remove // TODO Auto-generated method stub comments from your code
It is good that the onClick method has been marked with @Override.
Declare the onClick method inside the XML instead