Source: https://hobo.house/2017/07/17/using-italics-with-vim-in-your-terminal/
I wanted all code, system configuration file comments or in-line replies in neomutt email italicised to stand out easier. Many terminal emulators (xterm, xfce4-terminal, iterm2) don’t support [3m and [23m designators for italics but you can use a custom terminfo to do the trick. Here’s how to get it working.
You can run the following command in your terminal to see if it already supports italics:
echo -e "\e[3m is this italics? \e[23m"