I just plugged my iPhone in and instead of it being in English which it normally is, it's using German & I've not been to Germany. What can I do to get my preferred language back?
To solve a problem like this, I'd typically go to translate.google.com, type in "General", "International", and "Language", and translate them from English to German.
Or, sometimes I'm fortunate enough to have two computers/devices side by side, or I simply remember the user interface layout, and I navigate by menu item location.
I changed my iPhone 4 to run in German (Deutsch), and the German words are:
Einstellungen (Settings) > Allgemein (General) > Landeseinstellungen (Country settings) > Sprache (Language)
So just look for those words to navigate through Settings and change back to English.
If you have another iDevice with the same iOS version, you can use it as a guide to bring you back. While the command titles will have changed due to the updated language settings, the location within the menus will remain the same.
In this case, go through the following step by step on both devices to switch back to English:
Settings > General > Country Settings > Language
As @bneely notes, Google Translate can also be a very handy tool to figure out exactly what a particular phrase means.