I looked everywhere and did not see a bug reporter or Technical Issues area where I can report this, so I'm leaving this here hoping someone sees it.

Around June/July 2019, the achievement Fluent in R’lyehian on the Xbox One does not seem to be unlocking correctly. Many users on TrueAchievements are reporting that they completed the requirements of the achievement but aren't receiving the achievement as they should:

https://www.trueachievements.com/viewcomment.aspx?commentid=1232124

and

https://www.trueachievements.com/viewcomment.aspx?commentid=1223965

Solution appears to work up until June/July, when a spate of commenters indicated the achievement is no longer unlocking properly.