"They like Tanzanian light cotton wraps"
Translation:Wanapenda kanga za Tanzania
In this case, Tanzanian kanga(s) is translated as a kind of clothes belonging to Tanzania or Tanzanian culture so the particle -a is needed, I think. Then the agreement with the noun class completes the grammar according (za); remember that this particle needs the agreement with the noun that is preceeding it, the same as it occurs with adjectives and verbs.
Here is other example you can find in Duo:
Funguo za mlango (Door keys)
In this example, the agreement is according with the noun funguo and this is plural. When the noun is singular, the agreement changes: