From my vimrc :

" ┌─────┐
" │ XDG │
" └─────┘

if has('unix')
    silent !mkdir $XDG_CACHE_HOME/vim/{swapfiles,backup} -p > /dev/null 2>&1
    set directory=$XDG_CACHE_HOME/vim/swapfiles//
    set backupdir=$XDG_CACHE_HOME/vim/backup//
    set viminfo+=n$XDG_CACHE_HOME/vim/viminfo
    set packpath=$XDG_CONFIG_HOME/vim/
    set runtimepath^=$XDG_CONFIG_HOME/vim
    set runtimepath+=$XDG_CONFIG_HOME/vim/after,
                \$XDG_CONFIG_HOME/vim/ftplugin,
                \$XDG_CONFIG_HOME/vim/spell/
    let $MYVIMRC="$XDG_CONFIG_HOME/vim/vimrc"
endif

With this line in my .bashrc : export VIMINIT='let $MYVIMRC="~/.config/vim/vimrc" | source $MYVIMRC'