Don't see a big problem with that purchase.
The problem is simple. They just don't need it.
They have extensive office space in Mill Hill. More than enough for a translation commitee. If, for some reason, they needed to rent office space for the duration of the project in Wales then that would have much less of a cost attached to it than buying a luxury house.
To keep reminding the JW's to donate, donate, donate whilst purchasing a property like this is simply insensitive. Why oh why are such groups given tax free status when they can buy like this is unbelievable.
As pointed out above, Christ spoke of having nothing. This purchase again highlights how laughable their claims of being true Christians are.