Been a stupid thing America has done at least since WWI.

From a 1976 interview with German-American T. Max Kniesche, who moved to San Francisco in 1907, and worked in restaurants and cafes there:

Teiser: What was it like in San Francisco for Germans during the first world war? You were working at a clearly German restaurant. […]

Teiser: Did you change the kind of food that you served, or the decorations?

Kniesche: Well, the hamburger steak was Liberty Steak. French-fried potatoes were Liberty Potatoes. [laughter] We called it Liberty, but the liberty wasn’t there. Anyhow, everything went to “Liberty.” [laughter]

Sources:

• https://skeptics.stackexchange.com/questions/36579/did-the-u-s-government-try-to-rename-hamburgers-to-liberty-sandwiches
• https://archive.org/stream/schroederscafeger00knierich/schroederscafeger00knierich_djvu.txt