Has it ever happened to you that you change the language of vim’s spellchecker (:set spelllang=de), but when asked if vim should install the spell files you accidentally hit no? You can easily install the files yourself. Let’s assume you want to install German spell files. Execute

$ export LANG=de
$ curl -o ~/.vim/spell/$LANG.utf-8.spl http://ftp.vim.org/pub/vim/runtime/spell/$LANG.utf-8.spl