Disclaimer: Please follow this guide being aware of the fact that I'm not an expert regarding the things outlined below, however I made my best attempt. A few people in IRC confirmed it worked for them and the results looked acceptable.
If you installed infinality-bundle or the patched freetype2-infinality you'll most likely recently have run into an error relating to the harfbuzz package (>= 1.4.1-1), specifically something like: /usr/lib/libharfbuzz.so.0: undefined symbol: FT_Get_Var_Blend_Coordinates.
This is because the packages provided by the Infinality repositories or even the freetype2-infinality on AUR are and have been outdated for quite some time, since infinality-bundle's creator, bohoomil, has been missing/unresponsive for the past few months. freetype2 since has gotten new features and a changed ABI, one of which is a symbol named `FT_Get_Var_Blend_Coordina