Languages and Libraries
Here are some tips regarding what and how many languages and libraries or frameworks to use.
Programming Language
Deciding which exact language to use for a given project can be a very complicated task. However, many projects are created for an already established team or company, so the language you'll use is usually already clear or defined.
If you have to pick one yourself, brush up on what is currently used by other developers through forum searches, guides and similar resources. If you have freedom to choose a language, use whatever increases your and your team's competitiveness in the market while making sure you achieve the project goals.
Frameworks and Libraries
Always use as many frameworks and libraries as you can. The tech world is moving more and more towards codeless programming; the name of the game is developing faster, and the more work you delegate to these tools, the faster you produce results.
There are countless frameworks, and companies are always looking for people experienced in specific ones. It may be a good idea to choose different frameworks whenever you have plenty of time to develop your project, to gain as much experience as possible.