Not something I would use, but I really like the clean design of your hompage. However, in order to get a feel for what the app is doing, without having to read the explanation, I think it would make sense to have your screenshot in english, if the rest of the text is going to be in english.

I don't have an evil plan that everything should be in english , always. If your target market speaks another language, than go for that, but mixing the languages seems strange. I'm sure it's trivial to match the languages in the screenshot and text if you are trying to target multiple languages.