"Juma is cool."
Translation:Juma ni poa.
If I understand correctly, the m that are in front of some words is use to make a word singular (while wa is for plurals) such as mimi ni Mtanzania (I am Tanzanian) so using the m for poa would make since becuase an adjective can't be plural or singular. so wether I say Juma ni poa. or Juma na Emilian ni poa it would still just be poa because it is describing them (Juma and Emilian is good, well or cool). Hopefully this made sense.