@AnselmD: The German dictionaries that Sigil is bundled with (de_De) are optimized for Windows and
might cause problems with some characters such as curly apostrophes.
If you didn't install a custom German dictionary, try the following:
1. Locate your Sigil dictionary folder. (Default: C:\Program Files\Sigil\hunspell_dictionaries).
2. Make a backup copy of de_De.dic and de_De.aff and replace them with the files in
this attachment.
3. Retest the spellcheck of the words that you had problems with.
If replacing the dictionary files doesn't solve your problem, please attach your custom dictionary and give some specific examples of words that you have problems with.
(To locate the custom dictionaries, select Edit > Preferences > Open Preferences Location > user_dictionaries.)