What would happen if everyone spoke the same language?

There are around 7,000 living languages, and about half of them have fewer than ten thousand speakers, so the trend toward consolidation is already well advanced without anyone deciding it. A single language would reduce translation costs and lower the barrier to international collaboration, though the practical size of that gain is often overstated, since scientific and commercial communication already converges on a handful of languages. The loss is harder to price. Languages encode classification systems for local ecology, medicine and navigation that are frequently not recorded anywhere else, and the documented cases of ethnobotanical knowledge disappearing with a language are numerous. Language is also the primary carrier of cultural identity, and consolidation historically follows political power rather than convenience. Whether a common language would reduce conflict is exactly the kind of claim this file marks speculative — civil wars are commonly fought between people who share one.

How confident this is

This is speculation. The scenario is far enough outside anything observed that the answer depends heavily on which assumptions you start from — treat it as a thought experiment, not a prediction.

Society

• What would happen if everyone stopped having children? Schools would empty within a decade, the workforce would begin shrinking in about twenty years, and the last human would die in roughly a century.
• What would happen if everyone stopped eating meat? A large drop in agricultural emissions and land use, offset by disruption to a billion livelihoods and some regions with no alternative.
• What would happen if antibiotics stopped working? Routine surgery, chemotherapy and childbirth would all become far more dangerous — this is already happening slowly.
• What would happen if all jobs were automated? The production problem would be solved and the distribution problem would not — nobody has demonstrated the second half.
• What would happen if half the world's population disappeared? Not abundance — the collapse of specialised supply chains, because modern systems need specific people rather than a certain number of them.
• What would happen if the world's population doubled overnight? Food is the binding constraint — global production feeds around 8 billion, and doubling demand cannot be met from existing stocks.
• What would happen if everyone lived to 150? It depends entirely on whether those are healthy years — extended lifespan without extended healthspan makes almost everything worse.
• What would happen if everyone worked a four-day week? Trials generally show output holding steady with better wellbeing — but the results come from office work, not from hospitals or factories.
• What would happen if everyone drove an electric car? Urban air quality would improve immediately; the grid would need roughly a quarter more electricity, and mining demand would rise sharply.
• What would happen if nobody paid taxes? Everything funded collectively stops — roads, courts, defence, schools, health systems and pensions — within weeks to months.
• What would happen if all borders opened? Economic models suggest a very large rise in global output, and nobody can model the political response, which is the part that would decide it.