@FriedhelmW, can you post a screenshot or more detailed description of what you are seeing that is wrong? Or maybe another example? When I follow the link you provided, the article for Eugénie Grandet is the first result:
Eugénie is not bolded in the title of the result, but the article was found.
Searching in the upper right search box (the "Go" search) with Eugenie Grandet reveals a redirect to the correct page, which isn't helpful. However, a "Go" search for álbért éínstéín takes me to Albert Einstein so Go search is treating accented characters correctly for title matches.
The German language analyzer (which performs stemming and character normalization) for full-text search does treat e's with diacritics (specifically é è ë ê) differently than other vowels with the same diacritics. More details on that are in a comment on T104814.
Hopefully this is either not a problem, as Eugénie Grandet is currently found, or at least it is a variant of T104814.
On 26. Okt. 2017, 19:06 someone wrote a redirect without accent. Maybe this explains the different search result. Should we change the documentation which says that accents are ignored?
@FriedhelmW can you point me at the documentation you want to change? If you are referring to "Folds character families. Diacritical folding automatically matches foreign terms" then I agree it should be updated, but please be careful not to make it incorrect in a different way. Diacritical folding is turned on for most languages, though the set of characters that are folded differs from language to language.