IndexError (string not matched) : Conflict on key with plural and singular version not properly handled for JSON and YAML export

[jvigne]

To reproduce create csv file with the following wording to export in JSON or YAML.

key	fr	en
activerecord.models.user	Utilisateur
activerecord.models.user.one		User
activerecord.models.user.other		Users

Output
IndexError (string not matched)

Expected Output
Either give the priority to the singular or the plural version of the key. In any case display a debug log to inform users that there is a conflict.