Which programming language to learn to create a website?
The freelance web developer should start by learning the 2 basic languages of HTML and CSS.
Then it all depends on your specialization:
If you want to become a back-end developer: you will need to learn at least a language to communicate with the database (SQL) and a language to communicate with the server (PHP, Python or Go for example).
If you want to become a fullstack developer: you will have to learn all of this at the same time!
Which programming language to learn to develop a mobile application?
Again, several options are available to you. Indeed, you should know that the 2 leading operating systems on the smartphone market are iOS (apple) and android (samsung…). Both require different programming languages!
To develop an android mobile application, you will need to be proficient in Java. Note that the Kotlin is also used more and more.
To develop an iOS mobile application, you will need to learn Swift (recent language) or Objective-C (language that is tending to disappear)! Please note, to develop an iOS application, you must have a Mac computer.
Do you have a background as a web developer, and would like to create your android and iOS mobile application without having to go through learning Java or Swift?
Good news ! Today there are solutions for building cross-platform applications from web languages. Look at the technologies React Native, Ionic, Capacitor, Cordova or NativeScript, to name a few.