Vietnamese cannot use the same array of devices as can English in a cryptic crossword; that much is clear. Instead of trying to find 1:1 substitutes for each of the typical English devices, I think it best to start from scratch – though obviously there will be plenty of inspiration!
Whether to mark tone at all?
Marking vowel tones will make it harder to find crossing words when constructing. However, because tones allow for a pleasing array of wordplay, I feel they should be marked. Also, words can be crossed on letters which do not bear tone marks.
Tonal indicators
Hanoi Vietnamese has six tones. We have already decided that we want to mark tones fully in the grid. But should indication of tone in the wordplay be mandatory? I think not. It would lead to overly repetitive clue wording. A better idea may be to indicate tone only when changed relative to some base word or concept from the wordplay. Let’s take a simple example: ‘Ba’ can mean ‘dad’. ‘Bà’ can mean ‘granny’. Therefore, we can use ‘ba’ in the clue to get to an answer ‘bà’. But how? The tone of ‘bà’ is the huyền tone, which falls in pitch. It can be called (in English) a falling tone, meaning that anything from the rough semantic field of sloping downwards or travelling downhill (NB not falling over, which we will see is more appropriate to the ngã tone) may be used as an indicator. We are now in a position to suggest a pseudocode clue (I use ‘pseudocode’ to describe the use of English to give an idea of what happens in the final Vietnamese version):
Dad goes down hill and reappears as old woman
Here, the wordplay is ‘dad goes down hill’, the linker is ‘and reappears as’, and the definition is ‘old woman’. We can indicate this with brackets:
[Dad goes down hill] [and reappears as] [old woman]
We can further separate the wordplay into base and (tonal) operation on base:
[[Dad] [goes down hill]] [and reappears as] [old woman]
Importantly, the surface reading tells a story and is plausible on its own. Let us give the Vietnamese, which is entirely equivalent. Obviously we cannot use the same word in the definition and the answer, so we need to find a synonym (which may be literal or highly creative). In this case, we can go for the creative ‘his mother’, as grandmother would indeed be father’s mother. We thus avoid using the word bà in both clue and answer.
Ba đi xuống đồi; mẹ xuất hiện (2)
I have had to change the wording somewhat to make the Vietnamese more natural. The English translation is now ‘Dad goes down the hill; mother appears’. Note that now, the linker is at the end of the clue and the (cryptic) definition is in the middle. This is generally a no-no in English cryptic clues, but I have the initial intuition that it’s more obvious in Vietnamese which part (mẹ) is the definition and which part (xuất hiện) is the linker.
‘Ba’ can be called a regional word; it is not widespread in Northern Vietnam. To make the clue more difficult, we could consider taking the Hanoi standard ‘bố’ and adding a word alluding to the South. This could be as simple as rewriting the clue with ‘bố’ to begin ‘Southern father…’
Regiolectal tone indicators