This slogan was masively popularized by Marx & Engels, your socialist heroes. It is, however, incorrect to believe your heroes coined the phrase. Nope, just like money, these socialists depended on another's cleverness and productivity. They merely borrowed the phrase, to the extent that the true creator is utterly forgotten. She was Flora Tristan, a French-Peruvian feminist/activist who actually had working, paying jobs.
Accordng to Google, when asked "did marx and engels ever acknowledge flora tristan as creator of their popular phrase, "workers of the world unite?" Here's Google AI response:
"No, Karl Marx and Friedrich Engels never acknowledged Flora Tristan as the creator of their famous slogan, "Workers of the world, unite!" In fact, they never directly cited or credited her as the source for the idea of a universal working-class union. [1, 2, 3, 4]"
However, when Google is asked "who created the term "workers of the world, unite," Google AI replied: "The phrase was created by philosophers Karl Marx and Friedrich Engels. It first appeared as the famous concluding rallying cry in The Communist Manifesto, published in 1848. [1]"
No, it first appeared in Flora Tristan's book in 1843: "The Worker's Union."
That's the spoils of other peoples' money, apparently including Google AI's money: Deadbeatism. AKA: failure.