See [#2760134].

Try to run Google Translate (translate.google.com) with the sentence
Казнить нельзя помиловать.

Could you explain the strange results?

The tag is pretty strange, it's not about commas.

It is about commas.
https://ru.wikipedia.org/wiki/К...ьзя_помиловать
Казнить, нельзя помиловать — (казнить).
Казнить нельзя, помиловать — (не казнить, помиловать).
E.g.
http://tatoeba.org/rus/sentences/show/2260964

The same pattern:
https://en.wikipedia.org/wiki/I..._bella_peribis
http://tatoeba.org/rus/sentences/show/872383

Should I put a comma here and add another variant?

@Eldad
I can't explain the strange results. %(

@Marina,
Yes, do add a comma and then add another variant. Otherwise, I guess it cannot be rendered properly (and the current Russian sentence wouldn't mean anything coherent, would it? ;-))
Should I delete my own English rendition for the time being?

I think we can leave it as it is and add something like "to execute impossible to pardon" as a translation.
In the meantime, I'll add two variants with commas as well.

> #3789660
> #3789661

Thanks. The translation of the two sentences you added is a bit tricky. I'll try to attend to it later (or maybe others will precede me - Denis? ;-))

Of course, that was a literal translation. ;)

E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Punctuation.
The following advice of Bishop Orleton to Gourney and Maltravers in 1327 is an excellent example of the importance of punctuation:—Edwardum occidere nolite timere bonum est—“Refrain not to kill King Edward is right.” If the point is placed after the first word, the sentence reads, “Not to kill the king is right;” but if after the second word, the direction becomes, “Refrain not; to kill the king is right.”

See also comment on sentence: #3789022.

Может быть нужен тег, например "error" ?

Тут стоит comment on sentence, так что, я думаю, желающие разберутся.