[utnick]

Try to get a job or start a business in mainland europe without knowing another eu language besides english.

Knowing multiple languages is extremely valuable.

[tamas]

It is hard to get a job in mainland Europe without knowing English (as a developer). While the "another eu language" varies from country to country, the demand for English is constant.

[biohacker42]

No, the demand for language X + English is constant.

[tedunangst]

I know several people who have done exactly that without much trouble at all.