Greetings! I found a short info on contributing here: https://github.com/handsontable/handsontable/blob/master/CONTRIBUTING.md
Are you still open for it? What are your professional requirements for developers and their code to contribute?
Thank you!
Hey @n.schipkov
we are always open for PRs that meet those requirements 
however the hardest thing to address in those Guideliness are the logical aspects of programming. Like calling hooks in specified parts of plugins to keep their consistency.
Most of the merged PRs were related to small bug fixes, typos or .ts file adjustments. We usually do not merge new features as:
Do you plan to send over some ideas?
ps. we are eagerly for new language translations as well.
What languages are a priority for you now?
Here’s the list of supported languages https://github.com/handsontable/handsontable/tree/master/languages
It’s not bad, but we have Clients from all over the world so having all their languages would be perfect.