The next full pedia's release will be version 6 and the current Beta's, which are very stable, have been fully optimised for 64 bit technology only.
The Betas and the next version 6 release will run on:
10.12 Sierra
10.13 High Sierra
10.14 Mojave
Conor has only really been supporting pedia version 5.6.1 (macOS 10.5 to 10.11) in the look up search plug-ins area.
If you are able to upgrade your macOS I do advise that you do so not only for the new pedia's but also for the security and bug fixes present in the latest macOS. macOS upgrades are free. Even if you just upgrade to pedia version 5.6.1 it will run on macOS 10.12, 10.13 & 10.14.
From macOS 10.15, only 64 bit app's of any kind will run and Conor will be stopping any support for pre pedia's 5.6.1.
I do not know what, if there is any, cost of the pedia's upgrade path is from 5.5.2 or 5.6.1 to version 6, Conor will make this clearer in the
News & Announcement forum when he releases the full version 6 of all the macOS pedia's.