To languish is to wilt, pine away, become feeble. It always indicates an undesirable state. If you’re looking for a nice long soak in the tub, what you want is not to languish in the bath but to luxuriate in it.
The word “languid” (drooping, listless) often occurs in contexts that might lead people to think of relaxation. Even more confusing, the related word “languorous” does describe dreamy self-indulgent relaxation. No wonder people mistakenly think they want to “languish” in the bath.