In languages/i18n/en.json, the linksearch-text-ignored-domains' key begins with: Links to the following {{PLURAL:$2|domain is|domains are}} not recorded.
For $2==1, this yields: Links to the following domain is not recorded, etc.
This is grammatically incorrect. The verb refers to "links", not "domain(s)", so should always be "are" and never "is".