Sauerstoffflaschen

Also, the only word which would require an f-f-f-l ligature to print. This causes typeface designers to face a dilemma: do they make a special character for this one word, or do they let it be printed as "f ffl" and look a bit odder than it already is?

Source: "A Collection of Word Oddities and Trivia", http://members.aol.com/gulfhigh2/words7.html

Actually, the example is wrong. Sauerstoffflasche is a composite word, `Sauerstoff' meaning oxygen and `Flasche' bottle. There is a rule that ligatures can't connect parts of composite words, so the correct orthography is: Sauerstoffflasche, ff and fl being separate ligatures.

There is another crazy German example for the same problem: the meanings of the words `Wachstube' and `Wachstube' are different! (st == an st ligature.) The first one, Wachs-Tube, means waxtube, while Wach-Stube is guardroom.