Yes, English is on all signage at the parks (and signs in most tourist spots in Japan too, most restaurants have English menus until you get out of the cities and into more rural areas). Even street signs use the same phonetic alphabet so you can read it if you don't know the kanji.
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Trains give announcements in Japanese and English for the stops, though the manual informational announcements may not be in English. I just asked my husband again and he concurred the only time not speaking Japanese was a problem was on the trains. Students take compulsory English in school, so the younger generation especially tends to speak English and I have had students and CMs practice their English with me while we were in line. My trip in 2005 was WAY harder then it has been in the last few years - English has really sprouted up everywhere now.
I don't want to take us too far off track here (well.. further), but I've done both and had great trips. Our Tokyo board is kind of hidden under the "other lands" option:
https://www.disboards.com/forums/tokyo-disneyland.178/ Stop by there and I'm sure several people will be able to chime in also, even if you aren't planning a trip immediately (it's not like anyone can right now...). Or you can always DM me too if you want specifics...!
OK back to our regularly scheduled cruise program..!
