Seeking origin and original wording of a quotation attributed to Shakespeare

Question

During a Pub quiz early this week, a Shakespeare quote emerged in German translation, and I am keen to know the original wording and the work it stems from, or if it is possibly part of his notes.

This is my English translation of the line I heard in German:

Do not bemoan what cannot be altered but alter what is deplorable.

Original German:

Beklage nicht, was nicht zu ändern ist,
aber ändere, was zu beklagen ist.

However, I can't find an equivalent line anywhere. Is there one? (I searched fruitlessly on several sites, e.g., https://myshakespeare.me/shakespeares-works/search-filter/)

[Note that this was cross-posted on EL&U as well]

Answer 1

This is very similar (but not quite identical) to Ernst Ortlepp’s translation of The Two Gentlemen of Verona:

Proteus. Cease to lament for that thou canst not help,
And study help for that which thou lament’st.
Time is the nurse and breeder of all good.
Here if thou stay thou canst not see thy love;
Besides, thy staying will abridge thy life.

_{William Shakespeare (c. 1590). The Two Gentlemen of Verona, act 3, scene 1. Project Gutenberg.}

Proteus. Beklage nicht, was nicht zu ändern steht,
Und ändre, wenn du kannst, was du beklagst.
Die Zeit ist eine Amme alles Guten.
Verweilst du hier, so droht dir nur Gefahr,
Und deiner Liebe nüßt es nichts.

_{Ernst Ortlepp (1838). W. Shakspeare’s dramatische Werke, volume 1, p. 172. Stuttgart: L. F. Rieger.}

The version of these lines in the question may derive from Ortlepp’s translation by the operation of memory and fallible recall; the earliest instance I found on Google Books is from 2002.