slnunicode hasn't changed or been updated, and has no forum posts or bugs since 2006 [http://luaforge.net/projects/sln/]
ICU4Lua hasn't been touched since April 2009, and is at 0.2B. [http://luaforge.net/projects/icu-lua/]
That sort of status just doesn't inspire confidence in a language. I understand you can use it for game programming, or that you can write your own libraries for it, but that sort of thing doesn't encourage adoption.