I can tell, but that's because I can read both. Someone who's never learnt either language probably can't tell the difference between the sinographs, but could distinguish the language based on presence of hiragana, which are distinctly rounder and less dense

1. CN/JP aren't alphabets.(excepting hiragana and katakana) they're a logographic language, much like the Egyptian Hieroglyphs.

2. JP's kanji stole something like 95% of its characters from CN. the only real way to tell at a glance if a sentence is JP or CN is by looking for hiragana or katakana in the sentence, as JP usually has a few of them per sentence, while CN does not.

hope this helps your linguistic endeavours! :)

As someone who cannot read either language, I normally go by the rule of thumb that if it has a lot of curves it is probably Japanese, otherwise I assume it is Chinese. If we can throw Korean into the mix then I just need to see one circle and that's how I determine if it is or not. It's not a perfect system, but I would surmise that I can guess the language well above half of the time.

Also aren't the characters for Chinese shared across all spoken versions, if so, why did you specify Mandarin instead of just saying Chinese?

In contrast, do you know any words that are near identical when written down between two "alphabetical" languages based on their spelling?

Yes.

Idiot (English) Idiot (m) Idiote (f, French) Idiot (m) Idiotin (f, German)

On these charts, no idea.

In real texts, it's not that hard because Japanese text usually has kana in it. I can't read kana, but I can recognize some of them as being kana, even if I don't know what syllables they represent.

no

I wanna say 1 is japanese and 2 is chinese, based purely on which seems more complex and swishy.

I'm leaning towards the first one being Japanese and the second is Chinese.

Just based on hunch, I have no experience with either.

it's a list of characters (from left to right: japanese forms and traditional chinese forms). i can't tell fot all characters but it seems to be true for those i know. (?)

i don't speak any of these languages but i dabbled with learning to write ..

I can tell the difference, at least with simplified hanzi vs kanji, most of the time. When I was in Japanese language school, a lot of Chinese students would end up with small mistakes in Japanese as there are some other fairly minor writing differences. I can't remember if it was that Japan was more strict or the writing was taught slightly differently.

Across language, there are some fun coincidences in completely unrelated languages that have words that mean (nearly) the same thing with (nearly) the same spelling, though of course I can't conjure one from the depths of my not-yet-awake brain; I'm sure wikipedia or something. I think 'Interlingual homograph' is the term related to those. I still like Japanese letter (手紙 lit. hand paper) -> Chinese toilet paper and other fun ones in non-alphabetical scripts.

First one is weird, therefore Chinese.

Pretty sure weeb is the same in all languages