Wail! His dreadful language! (7)
I believe the answer is:
swahili
'language' is the definition.
(Swahili is an example)
'wail his dreadful' is the wordplay.
'dreadful' indicates anagramming the letters.
'wail'+'his'='wailhis'
'wailhis' anagrammed gives 'SWAHILI'.
(Other definitions for swahili that I've seen before include "Language widely used in East Africa" , "Language giving us bwana, safari" , "heard in parts of Africa" , "Language widespread in East Africa" , "Common language of E. Africa" .)