LemmaGenerator creates lemmatizers for several European languages that you can customize.

This package is available on Nuget:

Install-Package LemmaGenerator

This project was created by Matjaz Jursic and was retrieved on http:https://lemmatise.ijs.si/. He's the expert and did a great job so for all questions you should check his website.

If you just want to lemmatize words, you want to check the precompiled lemmatizer files here: https://github.com/AlexPoint/LemmaGenerator/tree/master/Test/Data.

Load the selected file in a stream a build a lemmatizer with it:

var dataFilepath = "/path/to/the/lemmatizer/file";
var stream = File.OpenRead(dataFilePath);
var lemmatizer = new Lemmatizer(stream);
var result = lemmatizer.Lemmatize("words");
Console.WriteLine(result);
// prints "word"

Note: Since this is an old Nuget, some newer environments may not support directly referencing the namespace after installing it via nuget.org. In such cases, you can add the .dll file from http:https://lemmatise.ijs.si/Software/Version3 into References of your project.

As mentioned above, you can customize your lemmatizer by using your own dictionary { word, lemma }. For more information, check Matjaz's website.