Determining the exact number of books written in each language is tricky due to incomplete records and varying definitions of what counts as a “book.” However, based on available data from library catalogs, publishing trends, and sources like UNESCO’s Index Translationum, we can estimate the top ten languages by book production. This ranking reflects both historical output and modern publishing, considering books written originally in the language (not translations). Here’s the list:

1. **English** – Dominates due to its global use, with millions of titles in major markets like the US, UK, and Commonwealth countries. Library of Congress alone holds over 17 million English books.

2. **Chinese (Mandarin)** – Massive output from China, especially post-20th century, with state-backed publishing and a huge population. Estimates suggest over 2 million titles.

3. **Spanish** – Widely used across Spain, Latin America, and growing US markets. Major publishers in Mexico and Spain contribute to hundreds of thousands of titles.

4. **French** – Strong literary tradition in France, Canada, and Francophone Africa. UNESCO data points to over 500,000 titles historically.

5. **German** – Significant output from Germany, Austria, and Switzerland, with a robust academic and literary publishing sector. Around 400,000 titles estimated.

6. **Russian** – Large historical and modern output from Russia and former Soviet states, with notable contributions in literature and science. Roughly 300,000 titles.

7. **Japanese** – Thriving publishing industry, especially in manga, novels, and technical books. Japan’s market supports over 250,000 titles.

8. **Portuguese** – Driven by Brazil and Portugal, with growing output in Angola and Mozambique. Estimated at 200,000 titles.

9. **Italian** – Strong literary tradition and academic publishing in Italy, with around 150,000 titles.

10. **Arabic** – Growing output across the Middle East and North Africa, though fragmented by dialects. Estimates suggest over 100,000 titles, boosted by recent digital publishing.

These numbers are rough, as they rely on catalog data, publishing reports, and estimates from sources like UNESCO and national libraries. English leads by a wide margin due to its global reach and historical dominance in print. Chinese and Spanish follow due to large populations and active publishing industries.