Having much more experience with language teaching than software, I think you might find this difficult. For one thing, it is very often extremely difficult, if not impossible, to make direct translations even when you know a language well and I would not under any circumstances rely on a machine to do this for you.
Language is much more about figures of speech than grammar or vocabulary! How do you really convey 'tranquilo' in English? is a very simple example.
Secondly, I agree that watching with subtitles is a valuable learning tool and I have used it myself both for teaching and learning, but please do not ever try to separate culture from language. The two things are so closely related it is impossible to say which came first.
Thirdly, there are too many homomyns (words that sound the same but are different). In fact, in English there are words that are even spelt the same and have different sounds and meanings. Take lead (pronounced led) - it's a metal and it's a verb, (pronounced leed), of which the past simple and past participle are led. How can a machine translate this? I think you would be better off with a good dictionary that translates both ways, plus a book/website that explains idiomatic expressions.
I would say that watching a film with subtitles is especially good for idiomatic expressions. It's a good way to know -this is how you express this feeling or idea in ...... language. Don't expect perfect translations as they don't exist.
In short, if such software exists, I would not trust it at all!
