Hi.
I consider myself to be a linguist and a Slavicist. I am interested in dialects and mutual intelligibility, and I am also a fairly big science fiction fan.
I am originally from the US. I immigrated to Australia in 2016 and have lived in Queensland since 2018.
“Is it the 2nd largest Germanic after English…?”
Yes.
“[B]ut just concentrated in Central Europe & not transcontinental like French, Spanish, Russian, Chinese, Portuguese?”
Chinese is no more “transcontinental” than German. The only people who speak Chinese on other continents are immigrant communities. German, in fact, is a bit more settled than Chinese in the Americas with many communities of native speakers in the US, Canada, and Belize that have existed since the 1700s.
Chinese is spoken natively mainly in China, Taiwan, and Singapore. There are small communities of Mandarin and Cantonese speakers in the US, Canada, Australia, and the UK. Most of those communities though, are relatively new.
Russian is only transcontinental because Russia spans two continents and has some former Soviet Republics in Central Asia. Russia is big and borders every country to the South between North Korea and Belarus.
The majority of four countries speak German natively: Germany, Austria, Switzerland, and Liechtenstein.
A substantial minority (38%) of Switzerland though speaks French, Italian, and Romansch.
“Is it however still more useful than Dutch or Swedish?”
If you are looking at “transcontinental” languages, Dutch is more useful insofar as it is also spoken in Suriname, Aruba, the Dutch Antilles, and there’s a mutually intelligible language in Africa called Afrikaans, spoken in South Africa, and by minorities in Namibia, Zimbabwe, and elsewhere.
That being said, Dutch and closely-related Afrikaans have fewer than a combined 40 million speakers. Most countries where Dutch is spoken natively are tiny with fewer than a million people, and there are lots of speakers of Creole languages in those countries.
German has more speakers than Dutch or Swedish. You will also find a lot more people in Germany, Austria, and Switzerland who don’t speak English than you will find people in the Netherlands or Sweden.
I have spoken German with many people who could not speak English and I wouldn’t have been able to communicate with them otherwise.
In most major cities around the world, there are Stammtische (conversation tables) of Germans and people who want to practice their German. Before I moved to Australia, I regularly attended one in Seattle. Obviously, with COVID restrictions, that’s changed.
With about 100,000,000 native speakers, German is a pretty big language. Only counting EU citizens, German is the biggest language in the EU by 15 million.