I'll test the french one with a couple I had to MANIPULATE to fall in love. They had no social for positive sim interaction, and one was even a Loner.

I'll report my test back.
Edit: Okay, it works very well. After reducing them to 0 relationship, and setting it to static, I tried romancing from both sides.
Toby: Tolea:
Loner Brave
Virtuoso Handy
Neat Hot-Headed
Green Thumb Athletic
Bookworm Loves the Outdoors
Their first interaction was positive, but then...It went south when Toby repeated a action. Then, they began getting negatives, so I sent Tolea and Toby twoards the insence, on a desk, and burned it. When it kicked in, I began doing every romantic interaction.They had the smallest amount for romantic interest I'd ever seen, at about a 15. They became BF and GF at the smallest possible amount. It's pretty safe to say this incense should be placed where you're wooing a NPC Sim.