Part of the reason for paying (aside from apple just wanting a nice little yearly fee), is that creating the paywall prevents the app store from being flooded with low quality, risky software that random users could download onto their phones. Additionally it helps the cut down the total number of apps that the approval team has to sort through, meaning that there is hopefully a shorter turn-around time on submitting an app for approval and actually getting positive or negative feedback.
And your second point, there is technically a language that can combine all the languages at once. If you weren't aware most modern programming languages are considered "high level languages". A high level language is easier for humans to read and understand by using words and easy abbreviations alongside certain well agreed upon rules and structure in order to minimize the amount of coding it takes to actually get to developing some software (I am vastly oversimplifying the reasons, but those are the biggest ones that come to mind at the moment).
What you are talking about here:
Also Swift maybe a good language but I feel there should be a langue that can combine all the languages at once.
Is known as a "low-level language". All high-level programming languages are built on top of the two most common types of low level languages: machine code & assembly languages. Without getting too in depth, machine code and assembly languages are the foundation of human's ability to interact with the machine.
So why don't we all write in assembly since that way we could just have one or two languages to worry about? Because it's extremely tedious, it's difficult to quickly build additional functionality, (to my knowledge) there are few security features to prevent malfunctions and prevent bad actors, and some of the rules for the languages differ from hardware to hardware depending on who your chip's manufacturer was. On top of that, it makes it very difficult to develop software for a wide variety of hardware.
Another reason there are so many languages is because each language has its own strengths and weaknesses, and depending on your project you should consider the inherent strengths of the language in question, as well as the maturity of the ecosystem (which means how many developers have been working to improve the core programming language as well as develop auxiliary software that add additional functionality), and their own skill in a particular language. Some languages are excel at being versatile, others are better at working with AI, and others are better in certain environments (for example websites vs a game for an apple computer).
If you combined all these languages you would end up with a highly versatile language...but you would invalidate the strengths of having specialties and special purposes. In fact you would honestly be better off just programming in assembly or machine code at that point.
I hope my explanation made sense.