So you seek to translate:
Ich möchte aus meinem Herzen hinaus
Unter den großen Himmel treten.
“I would like to step out of my heart,
And go walking beneath the enormous sky.”
I’ll start by putting in the missing accent marks 🙂
ἐκ τῆς καρδίας βούλομαι ἐκβαίνειν
ὑπὸ τῷ μεγάλῳ οὐρανῷ βαδίζειν
I am so, so not going to have anything to say about metre: never got the hang of it.
The Greek matches the English, but not the German. Notice that the Greek repeats ek– : “step out, out of my heart”; the German repeats the aus: “out of my heart, away”, but the verb isn’t there at all: it’s literally “I would out of my heart, away, beneath the great heaven to tread”. So I’d get rid of ἐκβαίνειν: the Greek should be as taut as the German.
The other problem is that ἐκ τῆς καρδίας sounds like “from my heart” (which in German would be von Herzen); in fact Aristophanes uses it in that meaning in Clouds 86 ἀλλ’ εἴπερ ἐκ τῆς καρδίας μ’ ὄντως φιλεῖς “but if you truly love me from your heart”.
Homeric/Poetic Greek is not something I’m in any way comfortable, but maybe ἑκάς ‘far away from’?
And for the ‘great heaven’, I’m thinking ‘broad’—cf. the Orthodox icon caption of the Virgin Mary as πλατυτέρα τῶν οὐρανῶν.
τῆς καρδίας ἑκάς βούλομαι
ὑπὸ τῷ πλατεῖ οὐρανῷ ἐκβαδίζειν
“away from the heart I wish
under the broad heaven to step out”
Someone else do the metre.