Hey Shaquille,

So you asked what languages & skills you will need to develop plugins and themes within WordPress.

tl;dr PHP, WordPress documentation, HTML, CSS, basic database manipulation/management

PHP

You will need to be comfortable with PHP because WordPress is built with PHP. Start there as it will give you an understanding of how WordPress does a lot of it's core functionality.

WordPress Documentation

From there, you should learn the WordPress hierarchy and how it basically extends PHP. WordPress has a lot of helper functions that you can use when making themes and plugins. For example, in WordPress there is a way to call in the header and footer of a theme.

HTML & CSS

After that you should learn CSS and HTML really well because that is what you are going to build your themes with.

You can literally take an HTML website, add some of those special WordPress functions I was talking about and have a 100% custom WordPress themes.

If you want to code plugins, you will need to be very familiar with PHP and WordPress' documentation.

Databases

The last skill you will likely need is a basic understand of how databases work. WordPress is database driven, and knowing how to set up a local WP install to develop on and then how to export and move that over to a production database will give you everything you need to make websites and plugins on the WordPress platform.