This photo came up on my feed and it’s a beautiful couple, but obviously not Tlingit clothing!  The reddit link shows that the original poster noted this and dug deeper - 

I found the photo at the Library of Congress. The catalog there doesn’t say anything about the couple being Tlingit, just says “Native man, seated, and woman, standing, facing front”, so I did some more research. Louis Shottridge and his wife apparently took a trip to Philadelphia in 1912 to meet another noted anthropologist and at first I thought that perhaps the photo was of a couple they met along the way, or perhaps someone that they met while in Philadelphia, but that was inconclusive.

So then I figured that I ought to search on the names. If I could figure out which group the names were from, then I could figure out what was up with the apparent discrepancy in the dress and the tribe. I did a search for Situwuka and found this information from the University of Pennsylvania Museum.

There I learned that Louis’ Tlingit name was Situwuka. The woman is his wife Florence. Knowing what Louis’ Tlingit name was helped me narrow my search terms down to this site which has another photo of them in this outfit. Apparently the couple were part of a touring group with some sort of Indian opera company where Louis sang tenor. The stereotypical look of the Indian is the Plains Indian look, which is of course what they have.

Thus the mystery of the Tlingit couple with the Plains Indian outfits is solved.