placeholder="{{'dso-selector.placeholder' | translate: { type: type.toString().toLowerCase() } }}"

https://github.com/DSpace/dspace-angular/blob/master/src/app/shared/dso-selector/dso-selector/dso-selector.component.html#L5

has a message in the catalog reading:

"dso-selector.placeholder": "Search for a {{ type }}",

https://github.com/DSpace/dspace-angular/blob/master/resources/i18n/en.json5#L535

Right now, it seems like these types (item, collection, commmunity, ...) are not getting translated.