Not quite. I would argue the total opposite in fact.

The cited study postulates in the discussion that Tip of Tongue events come from simple reduced frequency of use in any given word stemming from a much larger lexicon. There's no evidence at all suggest that there's actually a neurological disadvantage to bilingualism.

Also, it seems pretty counterintuitive to think that practice in an entirely new cognitive arena, something like a new language, could do anything but improve your ability to process language. If there's a paper out there I'd love to read it.

I wouldn't call that major

English is the only language that matters in today's world. The more fluent you are in it, the more successful you are likely to be.

Hardly. I think it can arguably said that in the Western Hemisphere and certain parts of the Eastern Hemispher knowing English is in general more valuable than knowing any other single language.

That hardly makes it the only one that matters. I personally have derived enormous benefits from studying Latin. There have been several times I have wished I spoke Spanish and a few times I had wished I could speak Japanese, Pashtun, Arabic, and Dari.

Knowing more languages is definitely a good thing.

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.

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.

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

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