whiteoctober/WhiteOctoberPagerfantaBundle — comment on commit 4165e4972770dcdf20e1f3fe4073243e05566de7
File: Resources/translations/pagerfanta.es.xliff line 3
By stof:

The symfony loader does not use these attributes at all. However, the source-language is required by the XSD schema of the XLIFF spec IIRC. But I don't know what the spec recommends when using keys.
and the target-language could help if someone wants to use an XLIFF editor to manage the translations so I think keeping it could be better (but it indeed requires updating it for new translations)