What are the disadvantages of fifth generation of language?

The major disadvantage of fifth generation programming languages is that these languages won't be as good as sixth generation languages.

It is also important to note that classification of programming languages in generations beyond the second generation is complete nonsense and nothing but a marketing hype; programming languages don't evolve in a linear succession, or one in the shape of a balanced tree, where each generation has common attributes and improvements over the previous generation.