I like your curiosity. I do not know what was running through Einstein's mind, I don’t think anybody does, but maybe we can try to understand the situation during that time. 

Einstein was a German, Jew born in 1879, moved to Switzerland at 18, introduced the theory of relativity at 26, and later moved to the US at 54 when Hitler came to power. He also helped create nuclear bombs. 

He wrote this piece in 1919, likely when he was still in Switzerland and while advancing his academia and scientist career 

Latin originated in Italy during the Roman Empire phase 8 BC. This was Old Latin and it had many variations. And then it went through all the famous philosophers like Cicero, different periods - medieval era, Renaissance era , Enlightenment era - tit started declining when the British empire rose to global power in the 17th/18th century but still used in academia and churches. 

During the widespread colonization (16th - 19th century), a prominent economic period was the transatlantic slave trade, with the Spanish and British empires capturing Africans for trade in South America. This period peaked around 19th century, leading to investments in slave trade companies like the South Sea Bubble. South America and the Caribbean experienced extensive colonization. One way to unite everyone was language and hence you see predominantly Spanish throughout the regions. In some regions, Portuguese and French are practiced, based on the colonizing powers. 

SEA has a long history of colonization since the 1st century, and only truly gained independence  the last 60 years. Prominent colonizers include the Dutch, Spanish, American, and British. The Philippines was colonized by the Spanish for 300 years. The Spanish-American War happened in the 1900 I think where the US won and they took over the Philippines and Puerto Rico. Spain also had colonies in Africa, including Morocco.

Eventually the world headed towards industrialization during Einstein’s time. This started with machinery, the Wright brothers just created airlines, phones were available but only to the upscale families in the 1920s (in the US, only after the 70s, it achieved 50% phone ownership rate). Communication was still limited. 

WW1 started at this point 1914 and it was the first time the US entered the global engagement. I believe after WW2, English became a globally used language due to the strong influence of the US - especially in international diplomacy, business, science, and tech. 

Plus the British colonized 50+ countries hence it must have come in handy. After the internet era begin post 70s, English became more of a norm

What we see now is probably an evolution of the language. But I do not know what was going on in Einstein’s mind when he wrote it. 
This is pretty much all I know