How similar is the Japanese spoken in Taiwan to the Japanese spoken in Japan? I've heard that Japanese is spoken by some Taiwanese people who were old enough to have lived during Japanese rule, along with some people who've learnt it for other reasons. For younger people, I've been told Mandarin or English would be the best means of communication, but I have a tendency to socialize a lot with retirees. How similar is the Japanese spoken in Taiwan by native speakers to the Japanese used in Japan? Did the two diverge after 1945? Are words that entered Japanese after 1945 also used in the Japanese spoken in Taiwan?

As far as I know, there is no difference, because Japanese is mainly used as a language to talk to people in Japan which is right close by, and to enjoy media and products from Japan. Japanese is still widely studied in Korea for the same reasons. Japanese textbooks in Taiwan seem to demonstrate an eagerness for fluency and avoiding confusion in business conversation.

Taiwan was under Japanese administration until 1945 and the language has not changed significantly since then.

On the other hand, the Japanese used in Hawaii and Brazil, among the lower-class immigrant Japanese communities there, may preserve some older forms. That immigration happened around 1900.