Important: Should you be working directly with Ubisoft or any of its chosen LSPs, please either contact your PM for more clarification, or refer to your Project Documentation. Should this be a part of a test or even an article (for a magazine, blog, or the like), heed the following paragraph.

The R6 series has -- over time -- established itself as a mainstay of e-gaming. At this point, translating its name would pose a grand disservice to the game itself, its fans and surely its impact on the scene (as total search results would be affected).
In addition to that, the title should be licensed as is.

(I shall upload all relevant links in a second, as I am writing from my cellphone.)


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Note added at 2 hrs (2020-03-22 11:50:32 GMT)
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References:

pt_BR
https://www.ubisoft.com/pt-br/game/rainbow-six/siege
https://globoesporte.globo.com/e-sportv/rainbow-6/noticia/ra...
https://br.ign.com/rainbow-six-siege/80216/news/rainbow-six-...

pt_PT
http://arena.rtp.pt/tag/rainbow-six-siege/
https://store.playstation.com/pt-pt/grid/STORE-MSF75508-TCRA...
https://pt.ign.com/rainbow-six-siege