His law ruined international language (7)
I believe the answer is:
swahili
'language' is the definition.
(Swahili is an example)
'his law ruined international' is the wordplay.
'ruined' indicates anagramming the letters.
'international' becomes 'i' (abbreviation eg in IMF).
'his'+'law'='hislaw'
'hislaw' with letters rearranged gives 'swahil'.
'swahil'+'i'='SWAHILI'
(Other definitions for swahili that I've seen before include "Major Bantu language widely used in E Africa" , "Widely-spoken Bantu language" , "An official language spoken in 15" , "Language widely used in East Africa" , "E. African language" .)