No one ask you to be the master of everything. Beginners?

Well that is you alone. I have been welding Java, Perl, Javascript, Shell scripts, Groovy for years in my work. All languages have their nuances, at the end of the day, they boils down to very big pieces of same concepts that are written in different syntaxes and semantics. You don’t have to know everything to be extremely versatile and creative in them. Even the one language Java has evolved so much across the versions.
If you think using one language alone will make you a full stack, think again. Even if you master all the languages, you are still not full stack.
Suppose after you have master Javascript, does it means you don’t need to know XML? You think it is just a markup language? Have you consider things related to XML, like XSLT, XPath, XML security? You think everything is communicated using JSON?
When you consider all these technologies standing between you as a tech master and a noob, what is so big deal about knowing 5-10 languages with intermediate to advance proficiency. We haven’t even talk about HTTP, HTML, CSS, Websocket, WebRTC, Ajax, Webaudio, and many more that falls under the entire web technologies umbrella.