A Japanese-English dictionary for Kobo e-readers

Here's the dictionary:
dicthtml-ja-en.zip

(last updated: 2023-01-24)

Installation

1. Plug your Kobo e-reader into your computer by USB, and open it on your computer in your file browser.
2. Copy the above zip file (without unzipping) into the directory ".kobo/custom-dict/".
   Note: some operating systems hide directories that start with period (such as ".kobo") by default. If you don't see a ".kobo" directory, configure your file browser to show hidden files. If you don't know how to do this, you can search online for instructions for most operating systems.
3. Properly disconnect the e-reader from your computer, as you would for any usb storage device. (For example, by first selecting "eject" or similar on your computer before physically disconnecting.)

Usage

After installation, you will have a new item in your Kobo's dictionary drop-down menu called "日本語 - English (Custom)". Select it to use this dictionary.

The dictionary entries look roughly like this (but with nicer rendering on the Kobo):

The entry header (at the top) consists of four parts in this order:

1. Pronunciation in hiragana.
2. Pitch accent, enclosed in square brackets. Not all entries have this, but most do. (The listed accent(s) are for standard Tokyo dialect.)
3. Written forms, enclosed in fancy square brackets. Generally the more common forms are listed first.
4. Grammatical information, in a comma separated list. This is always present for verbs and i-adjectives, but otherwise is (intentionally) typically absent. The rationale for this minimalism is that 1. this is a reading-oriented dictionary, and 2. most of the remaining grammatical information is either obvious from the translations and/or context, or it's something better looked up later in another resource anyway.

After the entry header is a numbered list of definitions/translations, generally with more common usages closer to the top.

If you select a single kanji character, there will also be a kanji entry, which is a bit different from a word entry. Kanji entries look like this:

The header shows an enlarged view of the kanji and a list of (rough) associated meanings. The katakana entries (separated by slashes) are the onyomi readings, and the hiragana entires (also separated by slashes) are the kunyomi readings.

Why?

Despite having an English->Japanese dictionary, the Kobo line of e-readers do not have an official Japanese->English dictionary available. Moreover, although there are some unofficial dictionaries floating around online, they seem to be hacked together based on shoehorning English definitions into the Kobo's official Japanese-Japanese dictionary. Although that approach works to an extent, it also results in a dictionary with clear limitations and a hacked-together feeling.

I wanted a clean Japanese-English dictionary on the Kobo, generated from scratch, that functions well out-of-the-box. So I made one. The result is the linked file at the top of this page.

Where did the definitions and other information come from?

The word definitions, name data, and kanji data are from the JMdict, JMnedict, and Kanjidic projects, respectively, all of which can be found here:
https://www.edrdg.org/wiki/index.php/Main_Page

The pitch accent data is from here:
https://github.com/mifunetoshiro/kanjium
(specifically data/source_files/raw/accents.txt)

Will this dictionary work with conjugated verbs and adjectives?

Short answer: it's not perfect, but it should work in most cases, yes.

Long answer: the displayed entries will always be in dictionary form, but the search index also includes basic conjugated forms to help find the right entries when you highlight words. Nevertheless, Kobo's dictionary search algorithm seems to occasionally fail at finding the right entries anyway. But most of the time it works.

Also, because of the duplicated entries for conjugations, Kobo will occasionally display duplicate entries when using this dictionary. But this is rare.

Disclaimer

Although I've tested this on my own Kobo e-reader, and it seems to work well for my own personal usage, I cannot and do not make any guarantees about its fitness for use. In other words, use at your own risk.