Honestly for the most part, not at all! When you enroll in the program, no matter what class you pick (Pop Culture in Anime, Japanese language, etc), the advisors will still teach everyone the basic phrases and etiquette ("thank you", "sorry", "how much is this?", etc) you need to know before classes start. Some of my classmates enrolled in the program knew little-to-no Japanese, yet they did just fine and had just as much fun in the country.
However, it does depends on where you want to travel. Outside of class, and mandatory trips, you're basically free to go wherever you want on your off-time. So if you're staying in the city the whole time, you don't have much to worry about because many restaurants offer English menus, train maps are in English, train announcers display and announce train stops in English, and many store workers and police at least know little/some English. As long as you use simple English, many will understand you.
If you want to go outside the city and visit rural areas, however, you will need to know at least a little conversational Japanese to get around, as not many restaurants and stores display prices in English, and not everyone knows English on the same level as people in the city areas. Despite this, as long as you have a 3G, 4G, or 5G connection on your phone, and access to apps like Google Translate, you should be fine no matter where you go. If you don't have these things on your phone, then try to have any friends (who know any level of Japanese) with you while travelling outside the city.
Honestly for the most part, not at all! When you enroll in the program, no matter what class you pick (Pop Culture in Anime, Japanese language, etc), the advisors will still teach everyone the basic phrases and etiquette ("thank you", "sorry", "how much is this?", etc) you need to know before classes start. Some of my classmates enrolled in the program knew little-to-no Japanese, yet they did just fine and had just as much fun in the country.
However, it does depends on where you want to travel. Outside of class, and mandatory trips, you're basically free to go wherever you want on your off-time. So if you're staying in the city the whole time, you don't have much to worry about because many restaurants offer English menus, train maps are in English, train announcers display and announce train stops in English, and many store workers and police at least know little/some English. As long as you use simple English, many will understand you.
If you want to go outside the city and visit rural areas, however, you will need to know at least a little conversational Japanese to get around, as not many restaurants and stores display prices in English, and not everyone knows English on the same level as people in the city areas. Despite this, as long as you have a 3G, 4G, or 5G connection on your phone, and access to apps like Google Translate, you should be fine no matter where you go. If you don't have these things on your phone, then try to have any friends (who know any level of Japanese) with you while travelling outside the city.