Recomended IntelliJ plugins
IntelliJ has an active 3rd party plugin market. You can probably find the language or feature you need by searching the market space. IntelliJ will additionally ask if you want to install available plugins for supported file types.
There are great plugins for Python, Perl, Rust, Ruby and many other languages and features.
If you are using Perforce, then there is a free community plugin available.
We use the Material Theme UI. We use the Material Solarized Dark UI theme for the screenshots on this site. We also use Pragmata Pro as our system font.