Sign Language is the key for an international language. Forget Esperanto! Besides sign language is quiet and useful in certain situations like underwater and opens the rift between deaf and non-deaf people. Made up international spoken languages paint people into corners and are more susceptible to mutation and you will always run into a group of people who can't make certain sounds! The hand would be the virtual-visual tongue.
The sign for dog in Russian, Chinese, English, Arabic, and Spanish would be the same!
Instead of trying to build a new language with grammar rules and such - sign language would be easier and abates many grammar rules. Think about it - build on the original language instead of coming up with new grammar and pronunciation rules which only confuse the brain.
Think about the middle finger, thumbs up, and peace sign?