Germans pretending to be american

It wasn't a case of different languages, but it happened relatively frequently in the American Civil War. Both Brigadier General Benjamin H. Grierson of the Union Army and Colonel John S. Mosby of the Confederate Army used troops that infiltrated the enemy lines with enemy uniforms. Also, in the Philippine Insurrection of 1899-1901, Filipinos either in the US Army or sympathetic toward the US were used to infiltrate insurrectionist leader Emilio Aguinaldo's headquarters and facilitate his capture, effectively ending the insurrection.

On one occasion, American troops in the European Theater in WWII actually turned the tables on the Germans less than three months after the Battle of the Bulge. The following is taken from Chapter 3 of The Bridge at Remagen by Ken Hechler, the same book which was the basis for the 1969 movie of the same title:

As the Ninth Army plunged toward the Rhine in the early days of March [1945], two interesting actions occurred whose meaning was not lost on the men of First Army. On the night of March 2, the 83rd Division quietly assembled a task force which consisted of all the German-speaking American troops that could be scraped together. These men donned German uniforms and discarded their olive-drab helmets for the black, low-cut German helmets. Tanks, tank destroyers, and other vehicles were disguised and camouflaged to look like German vehicles. Tricks like these had been pulled by the Germans during the Battle of the Bulge, and they had usually created a great deal of temporary confusion without much strategic success.

The trick worked better than anyone had hoped. The task force set out after dark on March 2, its goal the bridge over the Rhine at Obercassel, a suburb of Düsseldorf. The picked men slipped through the German lines, outwitting enemy sentries by fast talking when challenged. When dawn broke, the column was cautiously picking its way through the outskirts of Obercassel. A German motorcycle messenger challenged the column, refused to accept the hasty explanation, and raced his motorcycle back toward Berlin to spread the warning. Members of the American column vainly tried to bring down the motorcyclist with shots, but the firing only helped to alert the Germans that much quicker. Before long a fire fight had started in Obercassel. The American task force was strong enough to bull its way through this opposition. But the noise of the battle warned the town's chief Luftschutzwart (air raid warden). He set off the alarm that spurred the Germans to demolish their precious Rhine bridge just as American tanks were rolling up to it.