I read '6lang' as 'six-lang', which decomposes nicely to 'slang' in my ears. Of course, 'Slang' proper is already taken as the name of a programming language (as is 'S-Lang').
In the end, I mostly agree with https://blogs.perl.org/users/yuki_kimoto/2017/10/6lang-naming-proposal-is-good.html.
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