Why I'm getting this message: "Interface cannot be used (error 229)"
I found a solution: You need to download the ACS ACR122U Drivers for Mac OS X 10.x.

Here the download page and the direct link for PC/SC Driver Installer 1.1.0 (Mac 10.5, Mac 10.6, Mac 10.7, Mac 10.8, Mac 10.9, Mac 10.10) (2014-09-17 306KB).

You have to install it even if the installer is not properly signed.

It will install the useful driver in: /usr/libexec/SmartCardServices/drivers/ifd-acsccid.bundle

Now you are able to use the card reader.
If you want to test it out, I made a simple project here.