Non-trendy Saturday night dinner for two?
As for Chinatown--I enjoy Ocean Harbor for dinner. Most people go for Dim Sum but they have a full dinner menu. Penang and Banana Leaf are both malaysian. Practically same menu but BL has sushi and takes credit/debit cards. Chinatown isn't really a place for a QUIET dinner. It's more for atmosphere I think.
South Street--Alyans is decent middle eastern food--lots of fried things! YUM. cheap but very SMALL restaurant. It's on 4th street.
Here are two suggestions in Chinatown:
1. Pho Cali at 10th and Race. Not as polished a sit-down place as Rangoon (below). But it's inexpensive and very delicious. Here's a 2005 City Paper article about Pho Cali:
2. Rangoon at 9th right above Race. It's Burmese. Also inexpensive and very delicious. This is more of a sit-down place than Pho Cali.
For other choices in Chinatown, check out the restaurant page from the Philly Chinatown website:
As for South Street:
1. Mimosa on 9th off of South Street. BYO Italian. Reasonable prices. Not much decor, but it's good homemade Italian.
2. I've heard good things about Tamarind (Thai), but have never been. 117 South Street.
Hope that helps.