Here are some reasons why speaking English is a really great idea:

Language of engineering:
English is the language of engineering, with many engineering textbooks and technical documents being written in English.

Language of the environment:
English is the language of the environment, with many international environmental organizations using English as their official language.

Language of human rights:
English is the language of human rights, with many international human rights organizations using English as their official language.

Language of charity:
English is the language of charity, with many international charities using English as their primary language.

Language of religion:
English is the language of religion, with many religious texts and documents being written in English.