Question: when does the second half of vikings season 5 air?
Answer: 2018, in 2018

The fifth season consists of a double order of twenty episodes, split into two parts of ten episodes; the second half will premiere in 2018.  The premise of the fifth season differs from the previous four after the departure of Travis Fimmel as Ragnar, and it now follows the adventures of his sons. Jonathan Rhys Meyers is introduced as a major character, after his initial appearance in the fourth season's finale.