There's a similar phrase to "let's" in German. And it's sounds like:
"Lass uns"-when single;
"Lasst uns"- when plural
But when do we use "lassen Sie uns"?
The question is what to do with reflexive verbs? I mean can I say for example:
"Lass/Lasst/Lassen Sie uns sich unterhalten" for "Let's talk"
or
"Lassen Sie uns sich vorstellen" for "Let's introduce ourselves"
Is "wollen wir" the only option in this case and we can't use reflexive verbs with "lass uns"?
Lassen Sie uns... would be used in a formal context, like a Professor addressing his students using
Lassen Sie uns diesen Sonderfall mal genauer untersuchen...
Note sich etwas tun lassen is already reflexive - If you combine this with another reflexive verb in infinitive, things start to sound awkward:
Lassen Sie uns uns unterhalten!
Lassen Sie uns uns vorstellen!
Even if grammatically entirely correct, most people would avoid this awkward construct and evade into something like
Lassen Sie uns reden!
Machen wir uns doch kurz bekannt!
Stellen wir uns doch untereinander kurz vor!
(The doch here is a particle that comes quite close to the "Let's" meaning)
As a side note: Translating "Let's" as lassen Sie uns is not always optimal - there is a wide choice of possibilities that often tends to fit better
