Chap taking risks mostly on mountain ridge’s eastern tongue (8,7)
I believe the answer is:
mandarin chinese
'eastern tongue' is the definition.
'chap taking risks mostly on mountain ridge's' is the wordplay.
'chap' becomes 'man' (I've seen this before).
'taking risks' becomes 'daring'.
'mostly' means to remove the last letter.
'on mountain ridge's' becomes 'chinese' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'daring' with its last letter taken away is 'darin'.
'man'+'darin'+'chinese'='MANDARIN CHINESE'
(Other definitions for mandarin chinese that I've seen before include "World's most spoken language" , "Such languauge" .)