Although you can create non-English characters on a Mac without changing your keyboard layout, some may still prefer to enable a foreign keyboard layout instead. This may be faster than using the keystrokes for non-English characters, and it can help prepare you for foreign keyboards if you are going to study abroad. Here's how to do this:
1. Select System Preferences from the Apple menu in the Finder.
2. Under the choices for Personal, select the icon for International, as show below.
3. When the International dialog box appears, click the Input Menu tab.
4. Under Input Menu tab, scroll down and select the German (or Spanish) keyboard button. Be sure that the Show input menu in menu bar radio button at the bottom of the dialog box is selected to let you easily switch languages.
That’s it! You can now easily switch between English and German or Spanish keyboard inputs by selecting the preferred language on the menu bar (look for the flags!). Note that Mac OS X switches the language for all applications. Just select U.S. to switch back to English input.
See this article for a discussion of other options for creating non-English characters on your computer.