Thanks to Frenchman with one large tongue (5)
I believe the answer is:
tamil
'tongue' is the definition.
(Tamil is an example)
'thanks to frenchman with one large' is the wordplay.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'to frenchman' becomes 'm' (abbreviation for Monsieur).
'with' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'large' becomes 'L' (eg in clothes sizes).
'ta'+'m'+'i'+'l'='TAMIL'
(Other definitions for tamil that I've seen before include "Member of South Indian people" , "Asian language" , "Language of southern India and Sri Lanka" , "Southern Indian language" , "Dravidian people of India and Sri Lanka" .)