Fashionable alternation somehow becomes global (13)
I believe the answer is:
international
'global' is the definition.
(I know that global can be written as international)
'fashionable alternation somehow' is the wordplay.
'fashionable' becomes 'in' (in can mean fashionable or trendy).
'somehow' is an anagram indicator.
'alternation' is an anagram of 'ternational'.
'in'+'ternational'='INTERNATIONAL'
'becomes' is the link.
(Other definitions for international that I've seen before include "Global - game between countries" , "Game played between countries" , "Match between countries" , "Universal" , "Test (match)" .)