Others have already covered most of the 'just waaaaiit for iiiiit...' idioms that are most common in English right now. The idiom for precisely the occasion being mentioned in Turkish, though, is
A bride 'with cold feet' or a groom who 'gets cold feet' may jilt their fiancé(e) and leave them waiting at the altar.
Per Slate, Ben Jonson calqued 'cold feet' from an Italian idiom (freddo ai piedi, 'cold in the feet') about running low on cash that showed up in discussions of desperate, hard-up traders & gamblers. Stephan Crane repopularized it 300 years later in Maggie: A Girl of the Streets, where it had its modern sense of lost ardor and whence it became college slang and an imprecation against those hesitant to feed the idiocy of the First World War.
Usually you'd caution against getting cold feet (don't change your opinion at the moment) or comfort someone that 'people get cold feet all the time.'
Edit: Oh, I see a couple are still missing.
to avoid committing oneself.
Mr. Callaghan... is understood to have reserved his decision—or, in the current jargon, ‘kept his options open’. (The Guardian, 14 May 1969)
Church ain't out till they quit singin'
or many, many variations.
(Southern US) It ain't over till the fat lady sings.
As long as the organ is playing, church is not out. (The Daily Picayune, 17 October 1872)
Church is never out till the people get through singing... (The Fort Worth Gazette, 17 August 1894)
Church isn’t over until the choir stops singing. Anything can happen. (The Baltimore Sun, 1976)
(Southern US) It ain't over till it's over.
or, 'Where there is life, there is hope'.
Things can change.
It is said that, for the sick, while there is breath, there is hope. (Cicero, Letters to Atticus IX.x.3)
Were one only permitted to live, there would be hope. (P. Terentius Afer, The Self-Tormentor)
While there's life there is hope, and only the dead have none. (Theocritus, Idylls iv.42)