Now with support for the new block editor in WordPress 5.0!
SyntaxHighlighter Evolved allows you to easily post syntax-highlighted code to your site without losing its formatting or making any manual changes. It uses the SyntaxHighlighter JavaScript package by Alex Gorbatchev.
For a live demo, see this plugin’s homepage.
For a list of supported languages (most widely used languages are supported), see the WordPress.com support document.
Development of this plugin is on GitHub. Translation of the plugin into different languages is on the translation page.