Lua is as old as NewtonScript. Its authors have mentioned Scheme, SNOBOL, awk, bibtex, Icon, and (IIRC) Self as influences, but I don't recall them mentioning NewtonScript. Javascript also has a lot in common with Lua. I think it's because the trade-offs inherent in embedded scripting languages are making them converge on a similar overall language design, rather than plagiarism.

If you're putting Lua in a commercial application, the commercial application itself will provide the i18n, and Lua can use it with very little trouble. Lua's strings are raw byte arrays - you can load arbitrary binary data in them. A library that reads UTF-8 strings (say) can work with them just fine. (And while I don't speak Portuguese, there are examples in PiL that use it without problems.)

I disagree with you about whether metatables are annoying, but it's a matter of taste. I haven't ever used NewtonScript, but I do use metatables for quite a bit more than just prototype OO - it's easy to turn a table into a proxy + cache to a function, for example. Also, my Lua redis library (http://github.com/silentbicycle/sidereal) turns table reads and writes into syntactic sugar for redis db key, list, and set operations.