I think it would be much better to keep the languages synchronized, so the deaf people would at least have an advantage of easy international communication.

There is a story that a British ambassador once suggested to his Chinese counterpart that China should adopt the Roman alphabet, because it is much easier for schoolchildren to learn than the thousands of Chinese characters. European children learn the alphabet in kindergarten, whereas Chinese students are still learning new characters throughout the years of their education.

In response, the Chinese ambassador suggested that the peoples of Europe should all adopt the Chinese writing system. The "dialects" of Chinese are as dissimilar as Europe's various "languages", but their written form is largely mutually intelligible — so by adopting Chinese writing, all of Europe would have the advantage of easy international communication.