Bug 60427

Created attachment 74360 [details]
Test file with plain fi replacement, and without it using ZWNJ, ZWJ and ZWS

German typography could use zero width non-joiner (ZWNJ) characters to fix the automatic ligature handling of OpenType or Graphite fonts, see http://en.wikipedia.org/wiki/Zero-width_non-joiner.

LibreOffice has limited support for this feature, also there are problems with text search and spell checking, too, see the attached test file and screenshot. (It uses Linux Libertine G with automatic ligature replacement.)

Workaround for ligature handling: 
– try zero-width space (U-200B) instead of ZWNJ or
– use the font specific ligature settings (eg. "Linux Libertine G:liga=0" special font name) for the full word (or word part to keep ligatures in the other word parts)

Workaround for spell checking:
Specify ZWNJ with IGNORE feature of Hunspell in the affix file (it works with UTF-8 encoded Hunspell dictionaries):

IGNORE <U-200C>

where <U-200C> is the UTF-8 encoded U-200C ZWNJ

Plans:
LibreOffice/Hunspell:
– remove ZWNJ automatically for 8-bit encoded dictionaries
– add IGNORE ZWNJ to UTF-8 encoded dictionaries (English, Hungarian)

Linux Libertine G, Biolinum G:
– add/fix ZWNJ letter to avoid bad kerning (see screenshot)
– use short f for f + ZWNJ
– maybe it is better to remove the default ligature replacement for German (it is possible to set in the Graphite font)