Languages

My Japanese is bad, is it necessary to be know Japanese to visit in Japan?

To visit as a tourist? No. There are a lot of English language signage around stations and major tourist attractions, and lately more and more train station staff speak English if you want to stop to ask questions.

I would venture that 99% of tourists know no Japanese, or only know "arigatou gozaimasu", "ohayougozaimsu" and the like.

Even among the foreign residents, there are quite a lot who even after years speak only a very rudimentary Japanese.

You'll be totally fine as a tourists.

Don't worry. You will be fine. Several of my work mates have done just this. I would say that it's much more important to be able to use chopsticks :) If you are concerned then Google translate or similar on your phone can be a great help.

If you stick to major cities like Tokyo, Kyoto, Osaka, Fukuoka, and Hiroshima, and other places where many tourists go (for example, Nikko or Kanazawa or Hakone), you wonft have any serious problems. This doesnft mean you wonft occasionally have issues or some frustration. But nothing that would ruin your trip.

In the more remote and less well-known parts of Japan there will be a lot less support for foreign tourists (less signage in English, on-board train announcements in Japanese only, not many tourist information centers, etc.) Even then, you wonft be unsafe, but you could experience a higher level of frustration. I donft see any reason to include such places in a first-time itinerary, though. There are many wonderful places you can go where you can get by just fine without any Japanese. And even in the major cities, especially Kyoto, there are a lot of sites you can visit that arenft crowded, so you donft have to head to the hinterlands to get away from people. Go where the basic infrastructure (transit, hotels, restaurants, tourist information centers) is well developed, and then you can pick sites that donft attract many visitors, if you wish.

That said, you should do your homework ahead of time, have a well-researched itinerary and some backup provisions, and have some resources available for help if you need it (for example, a translation app and also a Help hotline number such as the JNTO Visitor Hotline https://www.japan.travel/en/plan/hotline/). The more you need to make last-minute changes and decisions on the fly, the more likely it is that you could get in a situation where the language barrier gets in your way.

Foreigners with no Japanese managed to travel through Japan 30 years ago without internet and with much less English around. Itfs all in your head.
Eg my mother Traveller around Japan alone for a week or so 25 years ago (no Internet, no mobile phones, no google maps) and managed to change some hotel reservations on the go and even went to far flung places like Hagi speaking no Japanese and no English but only a German dialect. But she wanted to be understood and she definitely was understood.

But if we all would need to learn the languages of all the countries we travel to the world would be full of polyglots (and probably a better place).