Hey Mnelson, I would definately not worry about the language barrier. I've been to all the parks and enjoyed it a lot. I found Paris and Hong Kong most all castmembers spoke decent English. In Tokyo, it was more simple english. Enough to help you to the bathroom or order food but not much more. But if you're ever in a pickle, they can get someone to translate.
As for shows and attractions, some are bilingual, some have different languages, and some are just not english at all. However that never really affected our appreciation for anything. If you are familiar with the rides in the US, their international counterparts are similar enough that you should be able to follow without an issue.
However there are 3 exceptions to this... Mystic Manor in DLHK, Tower of Terror in DisneySea, and the Phantom Manor in DLP. These vary a little or a lot from their US versions, and you may wish to ask a castmember to explain the story in english before going on the rides. They are awesome either way but it will add a bit if you know the story.
And I like your suggestion for an earpiece translator. If it's good enough for the UN General Assembly, why not Disney!