The release of the 1940 census has been much anticipated in the genealogical community. I am no exception. In terms of exploring your ancestors' linguistic heritage this census offers some good news and some bad news.
The bad news
For most people listed in the census information about the birthplace of parents and the language of the individual is not given. However, some individuals are singled out for supplementary questions. These questions do ask about the mother tongue of the individual and their parents' birthplaces. Unfortunately, there are no questions about the mother tongue of parents as was the case in the 1920 census.
The good news
If you are lucky enough to have an ancestor who was singled out for the supplementary questions, you will not only get information about the mother tongue of foreign-born ancestors, but also of American-born ancestors. Language questions were asked in four different censuses before 1940. In 1890 and 1910 the mother language of the individual was only given if the person did not speak English. In 1920 and 1930 the question concerned only the foreign-born population, so if you spoke Cajun French or Pennsylvania Dutch this information was not recorded. The 1940 census will be particularly helpful with groups that maintained their languages in the United States.
People working on Native American ancestry should be particularly aware of this question, as it will be the first time where you will have a clear indication about whether a native language was spoken in the household.
For more information about language in earlier censuses, check out this post.