Add missing i18n keys for OpenAIRE external sources.

[tdonohue]

References

• Adds missing i18n keys which are also referenced in OpenAIRE import from external source doesn't work DSpace#9501

Description

OpenAIRE is missing a lot of i18n keys, for example:

This PR adds them & removes a few keys which were duplicated

Instructions for Reviewers

• Check code
• Verify that this fixes missing keys that can be found in import from external sources

[tdonohue]

Merging this immediately as it's just missing i18n keys. We can follow it up with further fixes if more missing keys are found. Will NOT be backported to 7.x, as the missing keys are for features created in 8.0