I was born in the Netherlands, lived in Sweden, Finland, and now Germany. So, I always joke that I'm fluent in Dunglish, Swenglish, Finglish, and Genglish. I've also worked with plenty of native English speakers and have even been accused of having a vaguely Irish accent (due to having a few Irish friends). But usually my Dutch accent comes through quick enough that people can figure out where I'm from as soon as I open my mouth.

Learning languages is not easy and I never managed to master more than two out of the six or so I took classes in at some point (French, German, Latin, Swedish). I've also picked up a few words of Spanish by reading the relevant page in the lonely planet while traveling and by passively absorbing some words and phrases by watching e.g. Narcos on Netflix. But I'm not able to have an intelligent conversation in other languages than English and Dutch. I actually struggle to speak about work in Dutch these days because my brain is used to using English for that. My German is not that bad but I kind of sound like a moron when I mangle the grammar, use the wrong words, etc.

So, I avoid using it even though I've lived in Germany for 13 years now. This usually shocks people into some unhelpful advice "why don't you just ...". It takes non trivial amounts of time; time I simply don't have. That's why. I can order food, deal with bureaucrats (bureaucracy is optimized for idiots in most countries), etc. in German. There are enough people here reluctant or unable to speak English that this is useful. For everything else, I default to English. There's just no way my German will ever get to the same level. So, not going to bother with that. Improving my German skills would strictly be a hobby project and there's plenty of competition from more interesting projects for that time.

Picking a second language is kind of important for most people on this planet. I'd say English is probably the world's most popular second language and the most relevant one to master for doing business. In most corners of the world, speaking the magic phrase "do you speak English" will actually enable you to communicate. Even though the answer might be "no" (hey at least they understood the question), it kind of starts a process of figuring out who to use as a mediator and these tend to be people with some level of education and/or business influence. I.e. exactly those people you'd want to talk to generally.

There are a few other contenders for most popular second language: Mandarin, Spanish, Arabic, and maybe French on some continents. However, Mandarin only works in Asia (and migrant communities elsewhere), Spanish is limited to Spain and Southern America; and French limits you to France and their former colonies (mostly in Africa). Arabic is actually fairly widely spread thanks to migration patterns in the last few decades as well as the displacement of Christianity by Islam in a lot of former British, French, And Spanish colonies.

However, courtesy of the British, English has penetrated on all continents and is even an official language in several countries where it is definitely not the native tongue. It's kind of the modern era Latin and it has displaced that as the language of business, science, and diplomacy.

However, we are now entering an era of machine translations enabling people to communicate directly without having to master a second language. So, while still relevant, I'm guessing the world is going to be a bit bigger than the former spheres of influence of the British Empire and the cold war era US empire. I don't think a lot of people in the US or Europe will be learning Mandarin or Arabic any time soon. But I do think a lot of business will be conducted in other languages than English very soon. Automated translations will enable and facilitate this even for people who only speak 1 minor language.