How to know if two words have the same base?

Question

I want to know, in several languages, if two words are:

• either the same word,
• or the grammatical variants of the same word.

For example:

Answer 1

Snowball is a stemming API that can handle various natural languages and there are Snowball implementations for various programming languages.

http://snowball.tartarus.org/

Answer 2

Inflector.NET is an open source library that you can use to normalize the inflection of English nouns. Available at: https://github.com/davidarkemp/Inflector/tree/master/Inflector