You can coordinate with him to agree on which thread should be locked.
In my opinion, considering that dansus' topic is the oldest one, it would be advisable to have it as the official one and lock the other one.
However, Dansus' thread was originally for the previous year's contest. If he had edited it before the Taufik translation thread was published, it might not have been much of an issue. Since he made the edits after that, coordination between the original posters (OPs) on the same translation topic is necessary.
In my opinion, we must be fair to all members and avoid making the thread exclusive to AoBT members only, especially since in the following years, other users might not have a chance to provide translations — even if, for example, the previous year's contest thread hasn't yet been updated with a new one.