Two recent books remind us that we are what we speak.

What if every single tree, plant, flower and shrub was killed off and replaced by, say, iceplant? And what if not only California, not only the United States, but the whole world became entirely "English-only"?

Not a very appealing picture, yet it is precisely this all-too-possible future of "global homogeneity" that is evoked in a compelling new study, Vanishing Voices: The Extinction of the World''s Languages (Oxford University Press, $27.50), by two British researchers, Daniel Nettle and Suzanne Romaine. It is estimated that of the 5-7,000 languages existent in the world today, only 10 percent of them will survive the 21st century.

What is disappearing, of course, is not just the vocabulary and grammar of specific languages, but the contexts and communities in which they thrive. "Where languages are in danger, it is a sign of environmental distress," the authors note. When we speak of extinction, most people tend to worry more about animal species-- the larger and more attractive the better. (Never mind that human survival is much more linked to the continued health of plants and insects, whose extinctions go unmourned.) But the extinction of languages--many of which have highly evolved syntaxes and vocabularies that have grown out of unique ecological conditions--signals a loss of the "biolinguistic" complexity that has allowed life on Earth to thrive for so long.

Yet who gains the most from language extinction? And what is lost? A European explorer writing of his experiences in Papua New Guinea in 1912 sneered at the natives'' "hideous, snapping, barking dialect that passes for speech," adding that "noises like sneezes, snarls and the preliminary stages of choking--impossible to reproduce on paper--represented the names of villages, peoples and things." The explorer''s sarcasm was ill-advised, however, for who knows what information--about plants, weather cycles, family and community history--might be encoded in a unique language the European would like to see disappear, for fear of not being able to understand it. As the authors of Vanishing Voices dryly observe, "Traditional knowledge tends not to be valued as a human resource unless it makes an economic contribution to the West."

Indeed, the West''s most cherished institution, democracy, may be imperiled by the rise of monolingualism. As one of the thinkers the authors quote says, "Cultural uniformity is not likely to bring peace; it is much more likely to bring totalitarianism. A unitary system is easier for a privileged few to dominate." Variety, then, is not just the spice of a good life, but its prerequisite. Vanishing Voices is sure to encourage thoughtful debate on our political institutions and our cultural and economic priorities. (Californians will be especially interested in the authors'' observations on bilingual education.) "Modernization," Nettle and Romaine conclude, "does not have to entail loss of one''s language and culture, and local identity."

Totalitarian systems and the sense of escape provided by foreign-language instruction are very real to the young narrator of Madame (Farrar, Straus, Giroux, $26), a charming first novel by Polish author Antoni Libera, beautifully translated by Agnieszka Kolakowska. Warsaw in the 1950s and early ''60s is presented as "a bleak, poor world, sad, crude, boorish." The sensitive young hero, who loves theater, art and poetry, is bombarded instead with daily doses of "Communist zealotry, bombast, and wooden speech." The high school where much of the novel takes place offers a microcosm of a Cold War mentality: Censure, control, and absurd bureaucracies are the norm.

This is the world in which the narrator, "corrupted by literature and with [a] propensity to fantasize," falls under the spell of his beautiful French teacher. What begins as a schoolboy crush soon develops into a true obsession, however, as the narrator attempts to discover what lies beneath Madame''s "impregnable aloofness, formality, and icy calm." But his investigations reveal more than her past and her personal life, they lead him to his own vocation as a writer, an observer of the world. The mask of "concealment and disguise"--the mask of speaking in a foreign language--represents the French teacher''s "resounding, defiant refusal" to accept the reality of postwar Poland. "She was mute testimony to the ugliness and absurdity of our lives," the young narrator writes, "an eloquent reminder that it was possible to live differently." He learns that "it''s from language that everything flows" and that his "poor, gray world" can be "illuminated" by seeing it through a different perspective.

As the authors of Vanishing Voices write, "No language has a privileged window into reality." Our understanding of reality is shaped by the words we use to describe it. Another character in Madame, a young man who also fell in love with the French teacher when they were both in college, has the opportunity to travel to France. The experience is a revelation: "In France, even though he was nothing--a foreigner, and from Eastern Europe at that, without a penny to his name--he wasn''t afraid. He was serene. He was normal. He was himself." The freedom to be oneself--or to become a new self--lies at the heart of this intelligent and entertaining novel, which, like Vanishing Voices, reminds us that we are what we speak.