Japanese to English translation
You are not required to use the Japanese version of SMRPG to speedrun it.
English is about 9 minutes slower due to text render speed. English runners and Japanese runners share a leaderboard, but there are no time conversions.
You do not need to understand Japanese to run the game in Japanese. You need to recognize up to 40 item names and memorize 40 Dr. Topper quiz questions. You can do this with symbol recognition if you cannot read Japanese.
Reference lists
Cutscenes
If you would like to learn the game in Japanese, there are a few sticking points. Most of the text is just mashing, but there are a few times when you will have to pick an option. Most of the time, it's the 2nd option.
Mario's Pad: Item tutorial - 2nd option
Mario's Pad: Timed hits - 2nd option
Mushroom Kingdom: Mallow joins your party - first option
Midas River: Waterfall - 2nd option
Midas River: Barrels - 2nd option
Tadpole Pond: Frogfucius explanation - 2nd option
Moleville Mines: Mole conversation - 1st option both times
Moleville Mines: Minecart tutorial - 2nd option
Booster Tower: Switch tutorial - 2nd option (you will lose over a minute if you pick the first option)
Booster Hill: Tutorial - 2nd option
Birdo Fight: 1st option
Bowser Doors tutorials: Always 2nd option
The next thing to worry about is the item shops. There are a number of shops you will have to learn and you have two options. The first is to learn the text, and to recognize what J item corresponds to E item. Luckily for us, there's only a few items that share similar characters.
The practice app has a flashcard tool for memorizing items that appear in the Peach Chart.
Credit to The Mushroom Kingdom for all translations.
Items
Equipment
Peach abilities
Abilities for Peach once she hits level 15 at the end game, in case you don't remember. Geno Blast is the bottom of the first page, and Shocker is the first ability on the second page.
Memorization & recognition tips
If you don't know anything about Japanese, here is a basic guide that might help you with symbol recognition.
Distinguishing alphabets
Japanese has 3 alphabets that are each used for different purposes.
"Hiragana" characters look decently complicated and usually have curves and swirls in them.
Example:
あ い う お つ た ち さ な の ふ は... you get the idea.
"Katakana" characters are often simpler and are usually more pointy, angular, have more straight lines, and use less or longer strokes than Hiragana. The same letters as above would be written as:
ア イ ウ オ ツ タ チ サ ナ ノ フ ハ
Finally there are "Kanji" characters which usually represent an entire word and are very complicated (more than 4 lines). Examples: 花 海 青 宿屋
Hiragana (the swirly ones) and Kanji (the really complicated ones) are used to write out native Japanese words. They are sometimes used together in Dr. Topper quiz answers, like 海のいきもの where the first character looks much more complicated than the last five.
Katakana (the "simpler" ones) are used to write out the pronunciation of foreign words and are usually (not always, but most of the time) used on their own in Dr. Topper quiz answers. Katakana is also used in a lot of item names.
ハニーシロップ is pronounced like "ha-ni shi-rope", and when said quickly sounds like "Honey Syrup", which is what this item is.
You don't have to know these alphabets or what they are used for, but it might help you to distinguish them from each other.
For example:
Most Dr. Topper quiz answer sets that use a lot of Hiragana or Kanji will need you to pick the second answer. There are only a couple of exceptions to this, which you can memorize as exceptions to that rule. This covers a huge chunk of the questions. If you see an answer set you don't remember or recognize, and the second option has a lot of Hiragana, it's probably that one.
If the top answer is just 1 or 2 Kanji characters like 青 and 宿屋, that is always the correct one.
There are 2 questions where the top 2 answers are written in Katakana and look almost identical. These will throw you off even if you are otherwise good at guessing what alphabet the word belongs to.
If the top two answers start with キノ, pick the middle one. (These letters refer to mushrooms which are also used a lot in menus)
If they start with ヤリ, pick the top one.
Looking for specific characters
It can also help you to memorize what a couple of Japanese characters look like so you can tell them apart in menus and Topper questions. For example, look for ハ when looking for Honey Syrup, look for リ for Able Juice, etc etc.
This can also help with Dr. Topper questions, and extends to numbers and symbols as well as Japanese characters. For example:
If the top answer contains イ, choose it.
Any answer containing キノ is the right one. If two answers have キノ, pick the middle one.
If any answers contain a !, always choose the middle one.
If the answers contain numbers, choose ブキ９６ (middle), ４つ (middle), ３人 (middle), ７代目 (top), and １コイン (top).
There is one question that has "3D" in the bottom answer, but don't pick that one. Pick the top one that has no numbers.
There are 2 questions where all 3 answers start with ジ.
If you see a ・ in any answers, pick the bottom one.
Otherwise pick the middle one.
If all 3 answers start with パ, choose the bottom one.
Some other things you can do for Topper quiz
Create mnemonics for symbols that you think are easy to recognize. Pie likes to look for the Katakana symbols ト or イ and select the top answer, because he sees these symbols as resembling the letter T and uses the mnemonic "T for Top". He also looks for Hiragana characters that look like wheelchairs (such as お) and memorize answers accordingly. Flek sees ぐ and recognizes it as a reversed Pac-Man eating the right answer. Some runners like to recognize ヨ looking like a backwards E, or ツ and シ looking like smiley faces. You will come up with plenty of your own silly ones.
If you're using the practice app, you can start out by turning Hints on to show English translations of the Japanese questions. Some, but not all, of the Japanese questions were directly translated into English, such as the question about who leads the Axem Rangers. The position of the correct answer for these questions does not change from Japanese to English. If you use hints and see a question you recognize in English, you may make a mental association between some part of the Japanese question/answers and the English question you already know -- for example after using the practice tools a few times you might see the word レッド and remember "this is the one about the Axems" where in English you would pick the first answer. You would likewise pick the first answer in Japanese. This can help you get a head start when you're first starting out, since eventually you will be able to pick them out without thinking about the translation.
If you have no idea, 16 questions use the top answer, 16 questions use the middle answer, but only 8 use the bottom answer. Statistically go with the top or middle of you have to guess.
Marathon Game
If you can memorize 4 Japanese characters, simply look at the first character of the final line to determine their position:
ぬ = 1
す = 2
ふ = 3
な = 4
If this is too difficult, you can try looking for spaces between words:
1st: Top line of dialogue is one continuous line of text with no spaces. No numbers anywhere in the message.
2nd: Says the number 4 at the start of the second line.
3rd: Top line of dialogue DOES have a space between words. No numbers anywhere in the message.
4th: Says the number 3 in the middle of the second line, ends the message with a 2-letter standalone sentence "ちぇ。"
Items/Menus
As far as learning item names for shop/X and battle menus, it is much easier because you can learn them from just playing the game. It is easier to recognize items since they have icons to indicate the item type, and Equips filter by slot and character. You're not going to see a bomb icon and wonder if it's an Able Juice. The most difficult ones to distinguish are Ice Bomb (こおりだま) and Rock Candy (こんぺいとう) since they start with the same character and use the same icon. You can distinguish them by recognizing that Rock Candy has 6 characters and Ice Bomb only has 5.
If you have run the game before, item positions in menus have not changed. For example, if you're fighting Bowyer and scroll to your 3rd item screen and see a single item called
ツヨクナール where you would normally find Energizer, that's probably an Energizer. If you're on your first turn of an earlygame fight and you see a grayed out item called
ふっかつドリンク, that's probably a Pick Me Up. This will help you with most items, but you can use the practice app to keep your memory fresh on all of them since you will need to be able to recognize up to 40 items, and freebies, equip menu mistakes, and Box drop/RE freebie can throw you off.
If you haven't run the game before, you are probably using the wiki or pastebin as a guide through learning the route. The World Areas section of the wiki always shows both the Japanese and English names of items, equipment, and special attacks.