Whether to translate
映画 as “a movie”, “movies”, “the movie”, or “the movies” depends on the context and cannot be determined by its position in a sentence alone. However, word order does affect the focus of a sentence.
When there is no additional context,
私は映画を仕事のあと見た looks like a (bit redundant) response to a question about when the speaker watched
映画. In other words, the sentence somewhat puts
仕事のあと into focus. If it is indeed a response to such a question,
映画 must be old information to the listener. Google Translate might take that into consideration when it translates it as “the movie”.
仕事のあと映画を見た, on the other hand, looks more like a response to a question about what the speaker did after work.
映画を見た is put into focus. Then,
映画 is new information to the listener and “a movie” may be more appropriate.
But that’s when these are written as independent sentences. How they are interpreted in real life highly depends on the context and also on which part is given prominence when pronounced.