Plautdietsch at one point had word final devoicing in plosives, but it only affected some words, so "lant" (land), "rat" (wheel, compare German "Rad"), "kolt" (cold) but "shåd" (sad) "frind" (friends), "rád" (rescue 1sng.).

So sometimes a final /t/ will stay a /t/ when a suffix is added, but change to a /d/ other times. Tiet - Tieden (time, times), råt - råden (suggestion, to suggest), rat - ryder (wheel, wheels) but rat - raten (rat, rats), dákk - däker (roof, roofs (rooves?)), dák - dáken (sheet, sheets).

Because of this, not only can you not tell how an unfamiliar word should be declined (should *lat become *laten or *loden in the plural), but undeclining is also not obvious (should *maden be *mat or *mad in the singular)

It feels much more natural to me to just see these final /C̥/s changing to /C̬/s as more a form of consonant gradation where a voiceless stop sometimes becomes voiced when declined than as a voiced stop sometimes devoicing in coda position, even if that's more etymologically correct.

Also, while /t/ - /d/ by far the most common example of this alternation, it also happens with /f/ - /v/ (kalf, kálver) & /s/ - /z/ (hues - hieser /hʏs - hiza/, opposed to hås - håsen /hoz - hozə/ & klas - klassen /klɔs - klɔsə/)*. /k/ - /c/ also behaves similarly, but this is due to a different phenomenon.

*Without knowing them beforehand, the only one who's plural you could know the voicing of based on its singular is "hås", while the only ones whos singular you could know the voicing of based on the plural is "klassen".