How about adding some multiplier for language used to post.
Like English is most preferable and therfore can have some extra multiplier...
Also, posting off topic and newbies and other local boards can also have a multiplier...
I think this will give more accurate results here.
Also I don't know but is there a way we can get a current market price by comparing what the accounts are selling right now... This might be a bit difficult..
Well these are my suggestions ... Really good survice by the way.
Although this is primarily an english forum, I don't think posting in other languages should have an effect on the price. However posting in off topic, and politics (and maybe altcoins) will have a multiplier at some point in the future.
edit: I may be able to have it tell you what languages the account has posted in, but that won't effect the price of the account.
Or you can just make a chart or somthing to tell what percentage of post the user did in which board. This would effectivily tell the potential buyer if he wants to buy the account or not ... Moreover you can really easily pick this up from the user profile.