Translation:The women are beautiful.
But I'm guessing "여자 + 아이" can't be used in place of "woman" the same way "girl" can be used in American English?
여자아이 is used more to refer to young girls (children) from what I've found, and I've seen 여자 translated as both "girl" and "woman" in other places. So in Korean, it'd probably be more accurate to use 여자 instead of 여자아이 unless you're referring to an actual child.
And on a side note, "girl" in Korean could also be 소녀 (and boy, 소년). This was kind of messily typed out so I apologize if it wasn't very clear, haha
The term "girl" for a woman "is" acceptable for only certain ethnic groups in the U.S. to use.
Is there a difference between 아름답습니다 and 예쁩니다? Is one for people and the other for objects?
When "들" is added, does that always make it specific? As generalizations do not require "들"
-들 makes it a plural. without it it's not specified wether it's a singular or plural, could be one woman or several
~이 gives a specific subject. ~들 clarifies plurality. You are correct in that generalizations do not require ~들, but they'd use ~은 instead of ~이 since generalizations talk about a topic rather than a specific subject (like a particular woman or group of women)