我々 is a stiff word. Men use this word in a formal situation. われわれは断固戦い続けるべきである。We should continue this fight! 私たち is formal when the speaker is a man and it is formal and casual when the speaker is a woman. （a man）私たちは戦い続けるべきだと考えます。 I think that we should continue this fight.（formal） （a woman）私たちは戦い続けるべきだと考えます。 I think that we should continue this fight.（formal） （a woman）私たちは戦い続けるべきよ。 I think that we should continue this fight.（casual）

Thank you for Sensei's guidance and correction again! I've had a look in the website and it is really helpful! Free stuff do comes with shortage. I guess I'll just have to keep on learning the grammar so that I can spot the mistake made by the translation engine. As for now, it is still a great tool to help me deliver my message in another language (betting on readers' patience and kindness).

I can understand what TonyH wrote. It's true. Actually "どのような文脈では、「私たち」のために、この言葉を使うのですか？" is a strange Japanese. It should be "どんな文脈でこの言葉を「we」の意味で使いますか／使うのですか". But I can also understand what Kit wrote. Even though it is a strange Japanese, it would be helpful. By the way, I use this site: http://tools.planetleaf.com/trans/ . And I think that Nifty translation is the most natural.

Thanks Tony for the advice. I'm aware that Google tend to give wrong translation. But it's the only way I know to do it fast and free.