In English two space characters are used after the end of a sentence. But not in German. Usually no big deal because I type my text the way I want it. However, when I use commands to have vim reformat a paragraph for me it will insert two spaces when joining lines which start a new sentence. To avoid this a small setting in your .vimrc file can be used:
:set nojs " only one space after the end of a sentence
With this setting I can reformat paragraphs without having to check for double spaces afterwards.
