The wait has been long but I just got word (via Christian Henseler) that IBM yesterday released properly signed XTAF dictionaries for Notes 8.5.1. In case you're wondering "XTAF dictionaries" are the common dictionaries shared by Lotus Notes, Lotus Sametime and Lotus Symphony. Additional language dictionaries has been available for a while but the Eclipse feature wasn't signed so it was troublesome to install on client machines. The Eclipse features are now properly signed and they are easy to add to an update site and roll out using a widget catalog.
The bundle you need to grab from PartnerWorld or Passport Advantage is "IBM Lotus Notes XTAF Dictionaries 8.5.1 for Windows and Linux Multilingual (CZHE3ML)".