"Nous allons commander de beaux sacs."
Translation:We are going to order nice bags.
I'm afraid I don't really know how to explain it due to not being a native English speaker and thus not thinking in English "sounds", but there's a small difference between how "de" and "deux" are pronounced. Try putting them next to each other in for example Google Translate, press the listen button, and see if you can tell the difference?
"Gentil" means "nice" in terms of personality, not looks. Also "beau" isn't really limited to strictly one or two single words (see here: http://www.wordreference.com/fren/beau) so I think the translation of "nice" is just because it sounds better with this particular sentence. I think "beautiful" should be accepted too but I don't know if it is or not.
"We are going to request nice bags" is not accepted. Is there a special word for request? In English these two are pretty interchangeable.
I don't know. At first glance I would say "beautiful," but that is just my opinion. I don't see anything wrong with "lovely" so I guess it just wasn't the word they were looking for.
Also, I wouldn't say "lovely bags." "A lovely purse" perhaps, but not "a lovely bag" (Just me!). I think that "beautiful" is just a better word choice than "lovely."
The word "beau" has many uses and its translation to English varies slightly depending on the context. In terms of a product such as used in this sentence, "de beaux sacs" may be interpreted as choosing the ones of better quality, i.e., nice bags, good bags. "Beautiful" is left in for those who can't get past "beau=beautiful".