Ask HN: How do I get started for a NLP grammar corrector

I am learning Russian a third language and as a pet project I would like to develop a basic syntax corrector.

There are several resources online but it kinda gets overwhelming so I thought maybe some people here have relevant experience and can give me some pointers to narrow down my research.

What I would like to get into is:

1.Basic theory behind NLP and more specifically automated grammar checking 2. Open source tools/frameworks used for this purpose.

Thanks a lot.