Well! WordPress is known as a content management system CMS, which doesn’t require code language. But mastering the fundamentals of coding is essential for debugging, troubleshooting, and boosting the functionality of any platform. 

Sometimes you need to set up the client’s WordPress error logs, for which you need to know a bit about PHP. You might want to set external links on WordPress, so they open automatically, and then knowing the JavaScript is essential. Learning CSS and HTML is needed to customize a unique design for your client site.

Listed down the critical language, a WordPress developer should need to learn:

• CSS (Cascading Style Sheets) is used to enact how elements look. CSS cover page layout, color, font types, click effects, and other stylistic factors. Some HTML elements include CSS for body text to determine the color of the text. For example: {background-color: dark blue;}.
• HTML(Hypertext Markup Language) is easy to understand and one of the powerful code languages. It controls markup codes/elements to decide how different elements will be displayed on the page. Elements include headings, page titles, data tables, and paragraph text. 

Here a basic example of HTML<title>Understanding HTML</title> would set up the Understanding HTML as a title of the page.

• Javascript is used to create web pages, add a dynamic mode to them, and add special effects. It is used for validation and to perform complicated actions on websites. It also enhances the user experience by enabling the website to visitors.
  
  
• PHP is used for the behind the scene work of WordPress, and also called scripting language.