zero width (non) joiner glyphs are missing

[mjg]

The German language is (in)famous for monstruous compound words, which is why we should brake up ligatures at "interior word boundaries" to make these compound words more readable. The easiest (and standard) way to do this is to add a "zerowidth non joiner" (ZWNJ, Unicode U+200C) between, say, an "f" and an "l", in the same way in which one would add a soft hyphen, non breaking space.

Unicode definition