I'm currently working with Cisco TAC to resolve this issue when adding the French Canadian language pack after upgrading a customers UC520 to the UC520 8.0(0) - Software Package.
ERROR: Payload checksum [4898e6f40988a2c3d91dec5559077aa9] does not match registered payload checksum [78b2dbe63afea57b0cd124cb88500eb7] for cue-vm-fr_CA-langpack.uc500.7.1.3.prt1
The reason for my posting this is to advise anyone else who is having the problem that they are not alone! :)
Once my issue has been resolved, I'll be sure to post the solution.