a) Make sure that the |10n_multilang module is installed. This module is auto installed for Belgium, Swiss, Canada, ... but not for all countries.

Via Application App: search for "Multi Language Chart of Accounts" and install it (if not yet installed) 

b) Via App Accounting/Configuration/Accounting/Chart of account - export your CoA in your first language (f.e : US - export fields "id"+"name")
c) In your excel: put the id and the translation in the column "name" - second language will be f.e : FR

d) Change the language of your profile (via my profile) : put your user in language FR
e) Import your CoA in French. 

-> your CoA will be in 2 languages (US/FR).