Thuringe march 1945 probably,
-after the fall of France Indochinese (and others colored colonial soldiers) POW's were mainly in the Frontstalag of northern occupied France because the Nazis didn't want them on the german soil, of course perhaps we can find a small number in Germany too
-in southern free Zone the Indochinese soldiers were in the Repatriable Colonial Indigenous Military Companies (MICR), due the war and the lack of communications with Indochina France was unable to send them back home, so these companies of colonial military workers were raised for Senegalese Malagasy and Indochinese soldiers
after the invasion of the southern zone Germans didn't disband these companies and used them as manpower for the Organisation Todt (especially the Südwall) and others duties, I remember a book about the D-Day who the author described "Vietnamese" who accompanied german troops, I don't know if one of these companies reached Germany
"A Moi Auvergne"