It has been over 20 years since I wrote the the TranslatorRank code so I have forgotten a lot of the details. But as a first cut, I would divide the raw score by the age of the account, and maybe weight more recent activity over older activity. Brand new accounts would probably need to be handled as a special case.

Just out of curiosity, who would you cite as an example of a lame commenter with tends of thousands of karma points?