I am an American living in Germany.

This question of an official language is an annoying one. What do you mean by an "official language"? Is this for government things or for everyone? The counter point to this is why would you only want English only signs? What is the profit?
Here in Germany, all signs must be in German. This even in stores. In America, restaurants with menus in only one language, other than English, are consider authentic. Ex. French or Chinese restaurants. And why would you buy at a store in which you could not read the signs.
New York and California are two great examples of multi-language places over the years. America is an immigrant land. These places cater to people who are coming over here. You want to end all those small businesses.
Many places have signs in other languages. Even here in Germany there are bilingual places that have signs in more than one language.(This second language is only spoken by a few thousand people)
People don't want forms and brochures in a second language. Really, sometimes the people who need the service the most need help in another language. You mean you only want to help women who are batter if they speak only English.
You don't want the 40+ hour a week legal worker to get his taxes back. Are people exempt from laws if they do not speak English? It can take year to truly understand a language. Do you not want that person to participate in your society until they can learn your language?