Language of army reserves and militia (5)
I believe the answer is:
tamil
'language of army' is the definition.
'tamil' can be an answer for 'language' (Tamil is an example). I'm not sure about the 'of army' bit.
'reserves and militia' is the wordplay.
'reserves' becomes 'ta' (I've seen this in other clues).
'and' says to put letters next to each other.
'militia' becomes 'mil' (I can't justify this - if you can you should give a lot more credence to this answer).
'ta'+'mil'='TAMIL'
Can you help me to learn more?
(Other definitions for tamil that I've seen before include "Asian language" , "Native of south India or Sri Lanka" , "An official language of Sri Lanka" , "Member of South Indian people" , "Perhaps Indian" .)