The language barrier in Hong Kong Disneyland is nearly nonexistent, not something to worry about, however, visiting Hong Kong for the main reason of going to the park is in my personal opinion, not the best idea. Supplementing a trip to the city with a day at the park is good simply for the new experience.
The Cast Members at Shanghai Disneyland spoke an incredible amount of English. Nearly everyone we came across spoke English to the point I would describe it as fluent. I was immensely impressed by how easy it was to navigate the park with English. I went into Shanghai expecting the least amount of English and was shocked by how wrong my misconception was. I say this because I'm not sure if my view of Shanghai was biased, so take this with a grain of salt. I personally really enjoyed Shanghai and rank it at one of the higher spots compared to many other people who enjoyed it. However, once again, take this with a grain of salt. I visited when the park was getting hit by a typhoon and despite the weather, the park stayed open. The park was deserted. A couple of days later the crowds had returned and I still enjoyed the park. It has an atmosphere like no other park across the globe.
As for Tokyo Disneyland... My expectation of Tokyo was the exact opposite, lots of English speakers. However, we noticed that most of the Cast Members did not speak English, and those that did spoke very broken English. Tokyo's customer service is top-notch, and we never faced a true problem with the language barrier. However, I can add to what
@Minnie Mum said about the rule-following. It is entirely true. They will be very friendly about it, however, do not expect to be able to slide your way through most things like you could in WDW. All that being said, Tokyo was a tremendous experience and highly recommend it to all hardcore Disney fans given they have the opportunity. DisneySea truly is the greatest park in the world and it will continue to expand in the future.
Disneyland Paris is just behind Hong Kong in terms of the language barrier. Once again, not a problem. Once again as
@Minnie Mum stated, the Cast Members do not follow the constant smile regiment of American culture, which is perfectly fine as French culture is different and it is nice to appreciate differences. Disneyland Park is great, an expansion is warranted but all in all still a fun experience. As for the Walt Disney Studios named by many, including myself, as the worst Disney Park around the world. That does not mean enjoyment cannot be had from it, but do not expect the world from it. On the bright side, it is going to go under an enormous transformation which will greatly improve the resort's offerings.
The language barrier is not a problem at any of the parks around the world in my personal experience. While saying that it is nonexistent at the international parks is false, and expecting it to be nonexistent is also wrong, but I do not personally feel that any barrier detracts from the experience. Instead, I feel as though it adds to it. The individual languages and culture of the parks around the world add charm and make each of the parks special. After returning from the Asian parks I was sad in a way that I could understand everyone. As
@duder has previously stated, it is very peaceful and freeing being unable to understand anything.