The darker one is dated Sept. 3?, 1918, and he is "feeling fine, and all okay to date." The other one is dated April 12, 1919, dateline "Annecy" (a city south of Geneva, Switzerland) and says "You can expect Uncle Carl home about the 15th or 30th of June, as we are supposed to leave Brest [France] on the 1st of June. Best regards to all."
The opposite side of the cards shows the American and French flags intertwined, and two hands joined, with small pictures of a French soldier and an American soldier, and the caption in French "LA MAIN dans LA MAIN jusqu'à la VICTOIRE" and the same in English: "HAND IN HAND TO VICTORY"
The other card is captioned in German and French, and says "Bischöflicher Palast -- METZ -- Palais épiscopal." This is the residence of the Bishop of Metz, a city in eastern France that had been in German hands since 1871 (Franco-Prussian war) and by the time Uncle Carl arrived, would have been back under French control.