Rotten wooden floor

It sounds as if someone has replaced the rest of the floor in your bathroom already by removing timber and installing concrete. This often blocks vents which then cause rotting in the remaining timber. I would suggest your best permanent solution is to concrete the remaining floor area. however it is possible to replace the existing timber. Either way its likely to be two days work plus replacement of the floor covering.

Hello, of course it can be repaired, by removing the old wood and building a new one. that in maximum 2 days everything would be ready to use

If one part of the floor is concrete then it might be better to concrete the rest as if you replace the rotten wood with new wood it’s likely to happen again soon as the concrete usually blocks air vents & such blocking air into the floor however the rotten wood can be replaced with new if that’s the way you’d like to go this job shouldn’t take more then two days .

Two days work to replace a couple of joist and a bit of flooring seems excessive to me but I suppose each to their own. Point is yes it can be fixed. Will it cost a fortune? Well, shouldn’t but if you get lucky enough to secure a couple of quotes then it should set your mind to ease.