Translation:I thought you had gone to the movies.
The pluperfect subjunctive refers to the past as in DL's sentence.
The imperfect subjunctive is used for hypothetical statements about the present/future to express a mistaken idea (irrealis) and to soften requests in order to be polite.
This link has many examples of the imperfect. The last five examples are in the pluperfect subjunctive.
I don't know why the developers didn't map the relative pronoun 'que' in their algorithm for subjunctive statements. que=that and it is an more part of the eng translation to capture the ptg meaning. The correction routine accepts 'that' but doesn't use it. Very strange
well, we disagree. the word 'that' in the sentence above is a material part of its meaning. Without it, it loses the intent of the ptg original, ever so slightly I admit. the sentence is equivalent. Plus it refers to the subject ' eu ', thus it's pronominal too. Naw, nobody's every gonna make agree this is can be dispensed with in the translation. Sorry emeyr can't go with you on this.
You are disagreeing with grammarians. Read about "bridge verbs" in this link or try doing your own research in other sites. There is a lot of references to why the conjunction "that" can often be omitted in English. https://www.quickanddirtytips.com/education/grammar/when-to-delete-that