PROMT's Online-Translator.com might be what you're after:
- Have a shorter of way of transferring the web page data to the app: Simply enter the URL (see first screenshot)
- Be able to translate offline saved web pages: Ooops, got me. I'm not sure here, never tried that.
- Have a dictionary to check the validity of the translated words: You can use the integrated "Phrasebook" (second screenshot), but it also has dictionaries with grammar, phonetic and audio pronunciation.
With some (paid) addons, the app can be used even offline. It also supports voice input – and output (have the translation spoken via TTS). The big plus are its specialized dictionaries ("Topics" or "Categories"; they call it "Domain specific translation"), which allow for a much more accurate translation. I use their online service for a long time now (though I discovered the app only shortly), and am quite fond of it.
Search, Phrasebook, Translation (source: Google Play; click images for larger variants)