What programming language do you need to develop a web app?

If you want to develop web apps, you have to learn two programming languages (Javascript for the frontend and a language for the backend) at the same time, and you have to learn several other (simpler) formal languages also at the same time. p.s.
For More Information Please Refer:
https://www.quora.com/Is-it-advisable-to-learn-two-programming-languages-at-the-same-time
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