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Swift Programming in Japanese

This post is blog version of my talk on try! Swift Tokyo 2025. video link: https://www.youtube.com/watch?v=uVgxJpSvp-I Intro Programming has a history of over 50 years. Historicaly, source code has been written in English. Thanks to Unicode, modern programming languages support writing source code in natural languages other than English. Swift is a modern programming language that was launched 10 years ago. I tried Swift programming in Japanese. Based on my experience in developing this app App name: PlainShogi Board game app. It was released 3 years ago and has been updated continuously. Developed it using a standard setup: Xcode, Swift, and SwiftUI. By leveraging SwiftUI, I actively supported multiple platforms. What's Shogi? A traditional Japanese strategy board game. Played on a 9x9 board with unique piece movement rules. Known as “Japanese chess”. There are eight types of pieces in Shogi. enum Piece: String { case 歩, 角, 飛, 香, 桂, 銀, 金, 王 } This is the code of pieces. Swift allows you to use Japanese for identifiers. That’s pretty nice. I wrote the source code in Japanese so the pieces can be displayed as is on the UI. No additional code is required. I actively considered these approaches for this app. And I challenged myself to write almost all of the source code in Japanese. In this post, I would like to write based on the experience. What's “Swift programming in Japanese”? Swift source files are encoded in UTF-8. Swift is designed to allow non-English identifiers. Reserved words and framework identifiers remain in English. Using Japanese for naming identifiers. In this post, we will call this “Swift programming in Japanese”. Premise of this post Mac Xcode Swift Apple’s development tools and frameworks only No special tools and configs Based on my personal experience Out of Scope for This Post Advantages and disadvantages of non-English speakers using their native language for programming. Whether non-English speakers should program in English. Feasibility of Japanese identifiers Consider whether the character can be used as an identifier. Invalid characters Xcode will display an error message for invalid characters. It will also fail to compile. Let's examine characters by category. Hiragana Hiragana is the most basic character of the Japanese language. Counting by Unicode standards, there are 80 characters. All are valid. Katakana Katakana is similar in usage to italic fonts in English. There are 81 characters. All are valid. Kanji Kanji is Chinese characters adopted into Japanese writing system. In Japan, about 3000 kanji characters are used. All are valid. Symbol In Japan, these symbols are used. There are 32 symbols. With regard to symbols, there are characters that can be used and characters that cannot be used. Invalid Japanese symbols 13 invalid characters Comma and Period Brackets Symbols written at the beginning or end of a sentence These are generally unnecessary for identifiers Combining characters Unicode has a special type of characters. These are combining characters. Combining characters decorates one other character to create one new character. In Japanese, there are combining characters for the voiced and semi-voiced marks. These are valid. Alphabet Many Japanese do not speak English, but they use the alphabet. It is used in combination with other character types. Of course, the alphabet can be used as an identifier. Arabic numerals Arabic numerals are used in the same way. Of course, they can be used as identifiers. All Japanese characters These are all commonly used Japanese characters. However, there are many more characters in Unicode. If the number of characters that are actually used infrequently is included, the number is about twice as large. In total, there are over 6500 characters. Almost all Japanese characters are valid. Invalid characters are only some symbols. Does Swift compiler build properly? Here are some concerns that come to mind. Are there any bugs? Does it behave differently from English? Is there any performance loss? No problem at all. Does Xcode work properly? Here are some concerns that come to mind. Does it work as a text editor for Japanese in the first place? Will suggestions and other features work smoothly? Will Japanese fonts display properly? It is common to use identifiers as file names. Is it okay to use Japanese file names? Is Git built in to Xcode also okay? All of these are fine. Everything works properly. Test on Xcode XCTest requires identifiers to begin with “test”. This is a little disappointing. This has recently been

Apr 29, 2025 - 07:32

This post is blog version of my talk on try! Swift Tokyo 2025.

video link: https://www.youtube.com/watch?v=uVgxJpSvp-I

Intro

Programming has a history of over 50 years.
Historicaly, source code has been written in English.
Thanks to Unicode, modern programming languages support writing source code in natural languages other than English.
Swift is a modern programming language that was launched 10 years ago.
I tried Swift programming in Japanese.

Based on my experience in developing this app

App name: PlainShogi

Board game app.
It was released 3 years ago and has been updated continuously.
Developed it using a standard setup: Xcode, Swift, and SwiftUI.

By leveraging SwiftUI, I actively supported multiple platforms.

What's Shogi?

A traditional Japanese strategy board game.
Played on a 9x9 board with unique piece movement rules.
Known as “Japanese chess”.

There are eight types of pieces in Shogi.

enum Piece: String {
    case 歩,
         角,
         飛,
         香,
         桂,
         銀,
         金,
         王
}

This is the code of pieces.

Swift allows you to use Japanese for identifiers. That’s pretty nice.

I wrote the source code in Japanese so the pieces can be displayed as is on the UI. No additional code is required.

I actively considered these approaches for this app.

And I challenged myself to write almost all of the source code in Japanese.

In this post, I would like to write based on the experience.

What's “Swift programming in Japanese”?

Swift source files are encoded in UTF-8.
Swift is designed to allow non-English identifiers.
Reserved words and framework identifiers remain in English.
Using Japanese for naming identifiers.

In this post, we will call this “Swift programming in Japanese”.

Premise of this post

Mac
Xcode
Swift
Apple’s development tools and frameworks only
No special tools and configs
Based on my personal experience

Out of Scope for This Post

Advantages and disadvantages of non-English speakers using their native language for programming.
Whether non-English speakers should program in English.

Feasibility of Japanese identifiers

Consider whether the character can be used as an identifier.

Invalid characters

Xcode will display an error message for invalid characters. It will also fail to compile.

Let's examine characters by category.

Hiragana

Hiragana is the most basic character of the Japanese language.
Counting by Unicode standards, there are 80 characters.
All are valid.

Katakana

Katakana is similar in usage to italic fonts in English.
There are 81 characters.
All are valid.

Kanji

Kanji is Chinese characters adopted into Japanese writing system.
In Japan, about 3000 kanji characters are used.
All are valid.

Symbol

In Japan, these symbols are used. There are 32 symbols.

With regard to symbols, there are characters that can be used and characters that cannot be used.

Invalid Japanese symbols

13 invalid characters
Comma and Period
Brackets
Symbols written at the beginning or end of a sentence
These are generally unnecessary for identifiers

Combining characters

Unicode has a special type of characters.
These are combining characters.
Combining characters decorates one other character to create one new character.
In Japanese, there are combining characters for the voiced and semi-voiced marks.
These are valid.

Alphabet

Many Japanese do not speak English, but they use the alphabet.
It is used in combination with other character types.
Of course, the alphabet can be used as an identifier.

Arabic numerals

Arabic numerals are used in the same way.
Of course, they can be used as identifiers.

All Japanese characters

These are all commonly used Japanese characters. However, there are many more characters in Unicode.
If the number of characters that are actually used infrequently is included, the number is about twice as large.

In total, there are over 6500 characters. Almost all Japanese characters are valid. Invalid characters are only some symbols.

Does Swift compiler build properly?

Here are some concerns that come to mind.

Are there any bugs?
Does it behave differently from English?
Is there any performance loss?

No problem at all.

Does Xcode work properly?

Here are some concerns that come to mind.

Does it work as a text editor for Japanese in the first place?
Will suggestions and other features work smoothly?
Will Japanese fonts display properly?
It is common to use identifiers as file names. Is it okay to use Japanese file names?
Is Git built in to Xcode also okay?

All of these are fine. Everything works properly.

Test on Xcode

XCTest requires identifiers to begin with “test”. This is a little disappointing.

This has recently been resolved. In Swift Testing introduced in Xcode 16, there’s no need to prefix with “test”. That's great.

Answer of "Feasibility of Japanese identifiers"

So far, we have examined the feasibility of Japanese identifiers.

In short, Swift and Xcode fully support programming with Japanese identifiers!

Q: So, does everything work perfectly in Japanese?

The answer is NO.

Everything we have discussed so far has been about the inner workings of Swift.

Using Japanese outside of Swift can be risky

For example,

Xcode project name
Bundle Identifier
Name of File, Folder, or Target (* Only when using third-party development tools)
URL
Codable (* Only when decoding the data with other tools)

I told you earlier that file names are not a problem. However, please be careful when using third-party development tools. It is up to that development tool whether or not it supports Japanese.

Tips for code completion

In English, code completion is suggested with a single keyboard type. In Japanese, however, multiple keyboard types are required.

Tip 1: Keyboard shortcut

Display code completion using keyboard shortcut.

control + space
control + dot
option + escape

Tip 2: Using “self” or “Self”.

Using “self” or “Self” helps code completion work smoothly.

A medium-size issue: Naming convention

Case conventions are common. Names of types and protocols are UpperCamelCase. Everything else is lowerCamelCase.

However, there isn’t a well-established way to express these conventions in Japanese.

I tried various ways and searched online, but couldn’t find a solution.

* This issue applies to other programming languages as well

As an aside

Apple translates much of official information for developers into Japanese. They are very helpful to Japanese speakers with their high-quality translations.

Top page
Feature page
News
Video (title, description, subtitles)
Human Interface Guidelines

All of these have official Japanese translations. These provide strong support for Japanese speakers, especially in keeping up with OS updates + new devices.

By the way, Japanese translations do not exist for the API reference, tutorial series, and Xcode UI. Conversely, there are Japanese translations for all but these three.