'Were' is mostly used in the subjective mood, I think. Though sometimes I catch 'was' in speech, I still prefer to use 'were'.
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www.quora.com/Which-is-correct-I-wish-it-was-were-true :
"[...] In conditional sentences where the condition is unreal or not yet real and in that clauses after to wish, use were: I wish it were true that he loved me. Were is also used following "as if" and