Are there heuristics to tell if a character is from Chinese, Kanji, or Chu Nom?

Question

Suppose I know nothing about Chinese writing systems but some basic strokes and radicals. When given a blocky-looking character, how do I tell if it's a character only used in Kanji, in Chữ Nôm, or in Chinese?

Of course, we can also consider Sawndip, Tangut, Khitan, etc.

Clues I can think of:

• Chữ Nôm uses quite some radicals at places that Chinese characters won't use. For example, 𡨸 (Chữ in Chữ Nôm) uses 宁 as a left-side radical, which is never seen in Chinese.
• Simplified Chinese uses "又" quite often. For example, the traditional Chinese character 漢 (han in han zi) is simplified to 汉.
• Tangut and Khitan uses the two crossing strokes 乂 quite liberally.

EDIT: Updated the title to clarify that I'm looking for heuristics, rather than an "algorithm" that will prove 100% correct.

Disclaimer: As a native Chinese speaker who have learned Japanese and is recently dipping into Vietnamese, I found my own judgement biased and suffering from the curse of knowledge in coming up with an answer.

Answer 1

This is merely a heuristic, but Chữ Nôm characters tend to have non-traditional components in their construction, as a result of having to divide the character between a part that more or less unambiguously specifies the meaning, and a part that suggests the pronunciation. This sometimes leads to characters which seem more complex than a typical Han character, such as 𤄯 or 𠚢 .

You can see this in the character 𡨸 itself, which decomposes into a full phonetic 宁 and a full semantic part 字, which would be pretty unusual (although certainly not impossible) for a Han character.

Furthermore, in Chữ Nôm you may see Chinese radicals on the "wrong" side of the character — for example 𠊛 người has the 人 radical on the right hand side, which is truly unusual.

The above are naturally just heuristics, as many Chữ Nôm characters could well be plausible Han characters, even if they don't exist in the repertory of Han characters. 恄 ghét might be an example of such a combination that wouldn't be surprising at all as a Han character.

Answer 2

In general, you will need to look it up in a dictionary or in the Unicode standard, this is similar to the problem of guessing if a string of Latin letters represents an English or a German word. As in the case of Latin strings there are some hints that may help to identify a certain character as not belonging to standard Chinese, like the usage of a long obsolete radical or lacking some long established simplifications, but this applies only to a subset of the characters.

EDIT: In order to take the writing systems apart, I suggest another approach: Compile frequency lists of the characters for the languages you want to discriminate and use them for language identification (this is a standard task in Computational linguistics, and one where the computer is really good at). The most frequent characters will already provide a strong signal. This task is much easier than to identify the writing system for a single character in isolation.