Speak! Please?

I'll admit it.
I've been getting a bit paranoid about the twins and their language skills as their 18-month appointment approaches (It is scheduled for Monday, about three weeks late.). They seem to understand most everything: they run to their highchairs when I ask whether they want to eat; they bring us their shoes or go to the door when we suggest going outside; they can make a wide variety of animal noises on command.
But they just don't really speak.
They have a few clear words. (Well, I can't really think of any that are clear right now, but they do talk a lot.) They practice inflection frequently, usually imitating the true inflection of conversation. They rely heavily on nonverbal expressions, like when they shove books at us, put shoes on our feet or tug on our shirts if we dare try to read the paper, eat some breakfast or even just rest our heads on the table.
Yet when I listen to other toddlers communicate, it just isn't the same.
Despite our best efforts, Jonathan and Matthew are sinking quickly into the language of twinese with such sounds as "nah" for "done" (Where the heck did that come from?) or "seh" for "sit" or "da" for almost anything they want the other twin to see.
So, of course, I turned to Google.
And this is what I found.
According to this recent study, the boys might be behind in language speaking ability, but they are probably right on track as far as overall language development. As twins, they simply tend to use nonverbal skills more often than words.
In fact, they might have an advantage over singletons and twins who do not create their own languages. According to the authors, twin language (or twinese or idioglossia or cryptophasia) enhances language development in a way that is similar to the language enhancement experienced by bilingual children.
Now this study might be flawed.
It is based on a small sampling: the children of 26 mothers of twins and singletons.
But, who cares.
Before I Googled this study, I was worried that my boys might be behind in their communications skills. These folks say Jonathan and Matthew might, instead, be above average.
Their study is good enough for me.