I couldn't find a way to add supported locale as it seems they are hardcoded into main config file.
Adding it to "config/streams.php" doesn't work either because StreamsServiceProvider only merges certain items.
I am trying to add Turkish btw
Hey there! You could override the config by publishing the config but I would highly suggest you "Officially" add it like this:
Then you can start submitting translations with the aid of the Translation module: http://pyrocms.com/posts/2016/06/22/translator-module-v1-0