Would you rather... know how to speak only English or know how to speak every language but never English

Bilingual · Either

know how to speak only English

English serves as the de facto global language for international trade, aviation, science, and diplomacy, covering an enormous share of high-stakes interactions.
For anyone living and working in an English-speaking country, speaking only English creates virtually no practical disadvantage in daily life.
English is already widely understood as a second language across most of the world, making it the single most strategically useful language to retain.

know how to speak every language but never English

The majority of the world's population does not speak English as a first language; knowing every other tongue gives access to far more people and cultures.
If you can speak every language except English, you simply don't need it—anyone you'd want to speak English with also speaks something else you know.
Speaking to someone in their native language earns respect and connection that no shared lingua franca ever achieves.
The world's most widely spoken languages—Mandarin, Spanish, and Arabic—all remain available under option B, covering billions of people English alone can't reach.