By David Shepardson WASHINGTON (Reuters) -Lufthansa Chief Executive Carsten Spohr said on Thursday the German airline strongly backs U.S. airplane manufacturer Boeing Co, which has faced criticism over program delays. Earlier this month, Lufthansa said it would buy 10 cargo planes including seven of the 777X version, also known as 777-8F, and boosted its order for Boeing 787s. “Boeing as a symbol of America will get back to its feet,” Spohr said at a luncheon speech in Washington. He added to airline officials in attendance, “It’s a good time to negotiate prices with Boeing right now.” Spohr s…