Answer 1

This totally depends on you.
What do you want to do will answer your question.
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Here is a list:
Android Application -> Java

Webapp / Website -> HTML, CSS, JavaScript. And as you have Completed them, then you can learn AngularJS or NodeJS or PHP to do the backend stuff.

Windows Application -> C#

iOS Application -> Swift

Artificial intelligence / Machine learning / Neural Network -> Python

Game Development -> C++, C#

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And if you are not sure what to do, then get your hands dirty with Python.