EF Core 2.0 still has its conventions and it can change plural to singular and singular back to plural. Thus it definitely has the pluralization service built into it.
Yet I can't find this service to use it for other purposes.
In EF 6, I would write:
using System.Data.Entity.Infrastructure.Pluralization;
// Then somewhere in code
var englishPluralizationService = new EnglishPluralizationService();
var singularCat = englishPluralizationService.Singularize("Cats");
There is no built in pluralization in EF Core, but you can hook in for example the Inflector package: https://www.nuget.org/packages/Inflector/
I do that in "EF Core Power Tools" - see https://github.com/aspnet/EntityFrameworkCore/commit/dda3f43c046c2464f4813fdbb4261a6146aa4432 for more info