I don't like machine translator implants

[Roomba]

I think maybe just having them require a couple rare materials, like telecrystals or something along that line would work. Prevents people from just handing them out like candy for anyone who asks, requires a little bit of cooperation to obtain.

PDA chat is hard because there's no general robotics department, so the AI has to PDA message every borg individually to coordinate anything, plus it requires the borg have their PDA out at the moment to receive it. Also, it's only a little harder to monitor all PDA chat than it is to obtain translator implants.