Despite the USA’s history as a country of immigrants from many countries that spoke many languages, political bodies from city councils to state and federal congresses continue to consider “English-only” legislation. These laws range from identifying English as a common and unifying language to mandating that all government business and publications (including tax forms and voting ballots) use English and only English.
There is an important distinction to be made between those two general categories of language legislation. Many examples of such language legislation, such as an amendment to California’s constitution passed in 1986, only identify English as a common and unifying language, or even as an official language, but do not contain any restrictions on the use of other languages in governmental or other business (a copy of the amendment is available at http://ourworld.compuserve.com/homepages/JWCRAWFORD/prop63.htm).
The other category of language legislation does indeed specifically seek to restrict the use of non-English languages in governmental business and publications, from ballots and governmental forms to public schools (e.g. http://www.boston.com/news/local/articles/2003/10/12/family_adjusts_to_english_only_law/). These laws actively restrict the access of certain groups to the government, an act which has been found unconstitutional in a number of specific cases, such as with legislation in Alaska and Arizona (http://ourworld.compuserve.com/homepages/JWCRAWFORD/langleg.htm).
The more restrictive pieces of legislation are motivated primarily by the idea that bilingual governmental business encourages immigrants to avoid linguistic assimilation and therefore work to prevent social assimilation and that by providing governmental publications and conducting business in only English (especially in schools, for example) will help speed linguistic assimliation. Unfortunately, much of the other motivation is based on primarily prejudicial negative attitudes towards immigrants in general and seeks to discriminate against them unconstitutionally.
The USA has always been a country of incredible linguistic and cultural diversity. Furthermore, from the earliest days of our formation, government publications have been available in non-English languages. Evidence shows that even if or when such restrictive legislation is passed, enforcement is extremely limited (http://www.ocregister.com/ocregister/news/atoz/article_1150425.php). Furthermore, there is no evidence to suggest that restricting government business to English will help speed linguistic assimilation, but the first-hand evidence is overwhelming that such restrictive legislation will reduce access to government services and prevent residents who are not fluent in English from interacting with the government and related services in ways that serve not only to benefit themselves, but also society in general (e.g. social education, voting on propositions, etc).