Well, for starters, that particular picture is the most famous image of the Latvian legion.
As for the details, you can see the Latvian flags next to the German flag in the top right of the image, and you can also see that the soldiers all have the Latvian patch on their right sleeves.
Only foreign units had their national flag on their sleeves.
Those guys were Latvian SS volunteers and they joined late in the war, so it doesn't make sense to have them in a post about Weimar Germany.
As for the details, you can see the Latvian flags next to the German flag in the top right of the image, and you can also see that the soldiers all have the Latvian patch on their right sleeves.
Only foreign units had their national flag on their sleeves.