So many weird letters that's were barely used. á, é, í, ó, ú are more optional word emphasisers that barely anyone uses. And ë is the most common glottal stop denoter, ï less common. I can't think of examples with ä, ö and ü though, and they're more common in German as umlauts loanwords if any. :)
English also has all those letters, in loanwords, yet the map doesn't say so. The language does take over unusual letters in loanwords. For instance: I have seen English texts write oeuvre as œuvre like in French. It's also written like that in dictionaries.