Do you really give a thought when you say "Ruby is slow or Python is slow"? Just because Twitter moved their back end messaging to JVM doesn't necessarily make Ruby any slower than it already was. If a language runtime can't handle concurrent load or long running processes it is not a limitation of the language!
This is dejavu for me as Java was considered "a slow language" back in 1.1 days when HotSpot JVM was in its poorer life and ISO/IEC C++ was hot girl in town. Now that you realized your pony implementations can't catch up with real life performance expectation you start blaming languages, are you serious?
Whether it's global interpreter lock or lack of native threads it's the runtime (re-read the runtime) and not the language that is slow. For the love of technology, Stop blaming languages for poor performance of your suboptimal reinventions!
Every language implementor should at least consider the host platform support before coming up with their "Not Invented Here" approach, sadly that's what is happening with most modern languages.