In my first attempt, the algorithm guessed that my English dialect was 1. Singaporean 2. US Black Vernacular 3. American (Standard), and it guessed that my native language was 1. Vietnamese 2. Chinese 3. English.
Then I turned off my school grammar, including some generative grammar rules (from linguistics) in my head, and just truly went with my guts. This particularly affected the answers I gave to later questions. The second time the algorithm guessed that my dialect was 1. American (Standard) 2. Canadian 3. US Black Vernacular and that my native language was 1. English 2. Norwegian 3. Dutch.
This second set of results was very much off the mark but conformed to what I intended my answers to be.
My background: a native Thai speaker, born and raised in Thailand, started learning a bit of 'real' English at about eleven, lived in the US for two years when doing my Masters. I'm currently in Thailand but I mostly read and write in English for about fourteen years. My everyday spoken language is still Thai, but most of the movies, music, multimedia I consume are in English.
Possible implications:
1. Over-application of school grammar could result in unnatural use of language.
2. With enough exposure to proper language materials, non-natives can get pretty close to the native speaker in grammatical knowledge, even fairly subtle ones, at least according to the short and incomplete quiz here.
If any American English native speaker has time on their hands, I'd be grateful if you can tell me the differences between my writings (you can click on my username for more samples) and those of an educated native American English speaker.