Pete and T.J., the two guys in the Sonic commercials, relied on a linguist much more than their ad-libbing in the latest spot for the drive-in restaurant chain.

Sonic, which has featured the improvisational duo chatting in a car for a decade, decided to take a somewhat different approach from the usual ad-libbing and banter for an upcoming one-day event. For "Wingtoberfest" -- a one-day Oct. 15 special for half-price boneless wings -- the pair speaks German. English subtitles in the :15 and :30 spots and a web extra help viewers decipher the jokes and the deal.

Sonic launched boneless wings as a limited-time offer in October 2014 and expanded the line when they again hit restaurants this September. Chief Marketing Officer Todd Smith said they're set to become part of the chain's permanent menu in November. But first, Sonic wanted to figure out a promotion for the fall, especially as other chains are jumping on the seasonal bandwawgon with pumpkin spice lattes or Halloween-themed treats.

Margaret Johnson, exec creative director and partner at Goodby Silverstein & Partners, Sonic's agency for the last four years, said the shop checked with Pete and T.J. to see if they spoke German, and found out they did not.

Before shooting, the pair met with a linguist who was there with them on set to help with the dialog. The spot has a similar feel to the more traditional spots in the long-running campaign, but there is less word play and ad-libbing than usual.

"They sort of memorized what they were doing and then played with it for a little bit," said Mr. Smith. "It's hard to ad-lib in German when they don't speak it."

The spots will run beginning on Oct. 11 to inform viewers about the Oct. 15 special. Other campaign elements will carry a similar theme. "You'll see a lot of the social posts that we'll do will be in German as well," Ms. Johnson said.

In a web-only extra, the guys poke fun at their limited German and take on the Oktoberfest vibe in their clothing.