Again, Brussels is bilingual BY LAW (Belgium has 3 official languages, our capital city 2), that includes international companies. It's not a matter of what's preferential, it's a matter of what's a legal obligation.
Sometimes, it works out if you can appoint one person to the Dutch-speaking region of the country and another to the French-speaking region with both able to speak English but it's cheaper to find somebody who speaks all three languages.
I think you didn't get what I meant. Yes, I understand THE LAW says Brussels is bilingual but that's only for companies, not for every employee of the companies. Your cleaning lady doesn't need to know either language, by your own admission. I'm just saying that there are jobs that don't require one to know the official language of the country, be it Latvian, Dutch or French or all three. I assume you know that Latvian is the official language in Latvia but I'm not required to know it in my current job. I sure use it with my colleagues in informal situations but all the emails we send are in English (even to each other) and our interactions with clients are in English as well (because they're mostly from foreign countries).
Out of curiosity, I looked at our company's office in Brussels and what they're currently hiring. Some vacancies require Dutch, French, and English, some require English and Dutch/French, some say "Verbal and written communication skills in English. Dutch and /or French is an asset." So here you go, I just found a job in Brussels that doesn't require either Dutch or French