American volumes in Irish mostly (6)

'american volumes in irish mostly' is the definition.
I can't judge whether this definition defines the answer.

'volumes in irish mostly' is the wordplay.
'volumes in' becomes 'lit' (I can't explain this - if you can you should give a lot more credence to this answer).
'irish' becomes 'erse' (old-fashioned term for the Irish language).
'mostly' means to remove the last letter (most but not all of the word).
'erse' with its last letter taken off is 'ers'.
'lit'+'ers'='LITERS'

Can you help me to learn more?