my $.02:

don't let's - only BE
let's not - standard

You will find "don't let's" in areas/regions of the United States. It's not just BE.

Und dann gibt es noch die Variante "let's don't". Ich kenne sie von einer amerikanischen Autorin, und sie fällt mir immer auf.

Schnelles googeln brachte gerade keine brauchbaren Ergebnisse, aber ich meine mich zu erinnern, dass es eine regionale AE Variante war (Süden).

Es herrscht im Netz Uneinigkeit. Ich habe "don't let's" schon gehört/gelesen und hätte auch eher auf BE getippt.

http://www.bbc.co.uk/worldservice/learningeng...

http://en.wiktionary.org/wiki/let%27s#Usage_notes

You may also use don't, but it is often considered non-standard.

* Let’s don’t talk about it. (US)
* Don’t let’s talk about it. (British)

'There are steps down,’ said Jimmy… Don’t let’s,’ said Kathleen.
The Enchanted Castle, Edith Nesbit (UK, 1907)

I wouldn't say it's non-standard in the meaning "not good grammar"; afaik it is just a less common alternative to "let's not". I don't associate it specifically with any social group or time; you still hear people say it today in the UK.

LDOCE labels it BE: http://www.ldoceonline.com/dictionary/let-s

I think you would use it especially often when you have already started doing the thing that you don't want to do. For example: two people are arguing, and one says "But don't let's argue; why don't we have a cup of tea?".

Don't let's, let's don't.

Let's call the whole thing off.

Agree with #5 re BE (although the example from The Enchanted Castle sounds a bit odd (or jocular, at best) with "Don't let's" by itself, IMO).

Of course, there may be regional variation re the fuller forms with "Don't let's..." within the UK. Wonder if they sound wrong to Scots, for example? I'll have to ask around here :-)

AFAIK, "let's don't" is not used anywhere in the UK (and probably sounds strange to us Brits)...

EDIT: Have only just realised that The Enchanted Castle is from 1907, according to CM2DD, so that usage may well have been completely standard over 100 years ago :-)

“Don't let's” sounds like the language that genteel, well-brought-up characters would use in a Radio 4 play – I find it quite hard to imagine real people using it unselfconsciously and I can't recall ever having heard anyone say it in earnest. “Don't let's argue; why not have a cup of tea?” would be a nice way to defuse a row by shifting intentionally to an extra-polite tone.

Agree with #7 that "let's don't" is not BE.

I am familiar with "let's not".
I don't think I've heard "don't let's", but it sounds logical (= do not let us)
"Let's don't" don't sound logical (= let us do not?).