A friend in need is a friend indeed.
Is this actually an equivalent proverb? The German sentence seems to suggest something more like ‘in times of need, friends can’t be relied on’, which is the opposite of what the translation means. Hopefully I’m wrong.
I didn’t fully understand the german proverb at first (because the meaning of “Lot” is a little obscure), but a little google-fu brought up this explanation:
Das Sprichwort bedeutet, dass in einer Notlage Freunde sehr leichtgewichtig sind, denn jeder einzelne wiegt ja nur ein Tausendstel eines dreißigstel Pfundes.
Which makes sense. Further research brought up this page:
Freunde in der Not, gehen tausend auf ein Lot – Schreibung, Definition, Bedeutung, Beispiele | DWDS
In the examples below, someone wrote this:
Übersetzt heißt das, dass wir in Notlagen erkennen, wer wirklich unser Freund ist.
So the follow-up implication is that a friend who can be relied on in times of need truly is a friend. Which leads to the english proverb.
So the core message is the same.