Clarify messages about identical files and titles

Rephrased them to be less repetitive and more easily
readable and translatable.

Change-Id: I0f733a0a6d395c5869bae8d03b4b288539e4aa4e
Added more credits to the English i18n file

Change-Id: Ibf9a7a31457de282570902adc7b8af5f94758e3a
Merge changes Ibf9a7a31,I0f733a0a

* changes:
  Added more credits to the English i18n file
  Clarify messages about identical files and titles