hunspell VS spellsitter.nvim

You mentioned kinda like a con the online requirement, if you're interested in an offline method, try Hunspell. Otherwise, I just come up with this, is based on Google Suggestions API (even tho is not public):

i prefer and use hunspell

One can implement Huntspell which is what all browsers use (for example when typing in text areas). Is very simple and is C++.

Hunspell-based spell check

Excellent questions. https://github.com/wooorm/dictionaries here are some. The original dataset is here https://github.com/hunspell/hunspell#dictionaries

Since you are using already GPLv3: Why not reusing hunspell dictionaries/wordbooks? https://github.com/hunspell/hunspell

Those questions are open ones—and even the way they can be answered is unclear. Intuitively, Hunspell's suggestions are quite decent—otherwise, it wouldn't be the most widespread spellchecker, after all. A fair amount of "unhappy customers" can be easily found, too, in hunspell's repo issues. At the same time, one should distinguish between different reasons for the sub-par suggestion quality. It might be due to the algorithm itself, or due to the source data quality: the literal absence of the desired suggestion in the dictionary, or lack of aff-file settings that could've guided Hunspell to finding it.

Currently, Hunspell is maintained on GitHub (repo has only around 1k stars, will you believe it?). It seems that maintenance is not that easy if you'll weight the number of open issues and PRs, and the latest commits timeline: at the time of writing it (Jan 2021), the last commit to master was of May 2020, and the last release was 1.7 on Dec 2018. Hunspell's codebase is mostly "old-school" C++. It is being slowly modernized and it has very few comments; there are thousands of two-branch ifs to handle non-Unicode and Unicode text separately. There is also an attempt to rewrite Hunspell from scratch in a modern C++, which at some point was developed under the hunspell GitHub organization. Now it is independent and called nuspell (and, while not yet supporting all of the Hunspell features, already "achieved" version 4.2.0).

Thanks to the amazing work of lewis6991 and vigoux, spellsitter is now upstreamed to neovim core.

Use the spellsitter.nvim repository to implement.

There is also spellsitter you might want to look in https://github.com/lewis6991/spellsitter.nvim