Icons are not displayed in vim-airline and NERDTree

I've just installed plugins for my Neovim using vim-plug.  The plugins are working perfectly, but it's the icons within them that are haunting me.  I've provided screenshots of them below. NERDTree: vim-airline: They look very weird and it's hard to use.  Here's what I've tried: * Installed the plugin https://github.com/ryanoasis/vim-devicons * Installed https://github.com/ryanoasis/nerd-fonts#font-installation * Added this let g:airline_powerline_fonts = 1 I am using Debian Linux AMD64.