Ubuntu Japanese Localization: Complete Setup Guide for UI, IME, Fonts, Language Packs, and Locale

1. Benefits and Prerequisites of Localizing Ubuntu into Japanese

Goal of Japanese Localization — “Not Everything Becomes Japanese at Once”

“Japanese localization” in Ubuntu is not monolithic. In reality, the following layers are independent, and only when you configure all of them together will the system feel “properly localized”.

• UI Language (menus/dialogs): the display language for the desktop environment and settings UI
• Regional Formats: date / currency / decimal separators / first day of week
• IME (Japanese input: Mozc, etc.): actual Kana/Kanji conversion input layer
• Fonts (Noto CJK / IPA, etc.): legibility, glyph shape, dotted accent clarity
• Per-application language packs (LibreOffice, etc.): sometimes a separate package is required
• Locale (LANG/LC_*): terminal / encoding / message language control

Because of this layered structure, it is completely normal that some parts remain English even when you chose Japanese during initial setup. This article explains how to prioritize GUI configuration first, then install required packages and perform small adjustments afterward to practically approach “complete” Japanese localization.

Benefits of Japanese Localization

• Higher work efficiency: Understand settings and error messages in Japanese → faster troubleshooting.
• Consistent notation: dates, numeric formats, currency notation match Japanese standards → fewer misunderstandings when creating docs or notes.
• Better readability & visuals: correct Japanese fonts eliminate smudged dots or awkward spacing.
• Lower learning cost: easier to read help texts and operational explanations in Japanese.

Required Time and Knowledge

• Estimated duration: about 10 minutes for GUI only, 30–40 minutes including extra packages and fonts.
• Knowledge requirements: basic settings UI operation + a few terminal commands (copy-and-paste is enough).
• Re-login / reboot: language and IME changes often require re-login, and sometimes full reboot.

Recommended Pre-Setup

• Internet connection: required for language packs / fonts / IME packages.
• Software updates: update package indexes to ensure smooth installation.
• Admin privileges (sudo): required for installing additional packages.

Why Some Parts Stay English Even After “Japanese Localization”

• Distribution differences: Snap/Flatpak distribution format may store language resources separately.
• Individual language packs: e.g. LibreOffice requires a -l10n-ja separate package.
• Locale not configured: terminal and some apps stay English → fix by configuring locale.
• IME integration: Mozc not added to input sources / no re-login → conversion does not work.

How This Article Proceeds (Preview of Later Sections)

1. Japanese localization via GUI (fastest way to feel the effect)
2. Install language packs / IME (language-pack-ja and ibus-mozc)
3. Font optimization (Noto CJK for improved legibility)
4. Per-application Japanese localization (representative cases and patterns)
5. Pitfalls + checklist (eliminate “only some parts remain English”)

First, localize the big picture via “GUI settings,” then IME and fonts make it actually usable. Finish with per-application and locale adjustments — this order is the least confusing and the most reliable.

2. Apply Japanese Settings via GUI

Why Start by Localizing the “Visual Layer” First

Japanese localization in Ubuntu dramatically changes daily usability just by switching the GUI language.
This is the fastest way to feel meaningful improvement.
Especially in the GNOME desktop environment, these settings become the premise for later IME and font configuration.

Steps to Localize from Settings App

Assuming Ubuntu desktop environment, the standard flow is as follows.

1. Open “Settings” from the dock (bottom-left or left panel)
2. Click “Region & Language” from the left sidebar
3. Under “Language” → select Japanese and click “Install”
4. Under “Formats” → switch to Japan
   → this switches date / decimal / currency rules to Japanese standards
5. Sign out once, then log back in

This alone changes menus / settings labels to Japanese, drastically changing the UX.

Why “Formats” Must Also Be Set to Japan

Even when “Language” is Japanese, “Formats” often stays English.
This is a common root cause of typical issues:

• Decimal separator behaves “.” vs “,” inconsistently
• Date remains in “MM/DD/YYYY” format
• Currency symbol stays “$”

Unifying both Language and Formats to Japanese/Japan fully aligns display rules.
This matters especially for people dealing with numbers or writing technical posts.

Re-login vs Reboot — Rules of Thumb

• Language pack reflection → usually re-login is enough
• IME and some app messages → sometimes a full reboot is needed

Guideline:

Checklist You Should Confirm Here

• Settings → Region & Language
  → Language = Japanese
  → Formats = Japan
• Did you actually sign out / re-login after changing?

At this point, the “visible part” of Japanese localization is mostly complete.

3. Install Additional Language Packs (Ubuntu Standard Packages)

Why GUI Alone Is Not Enough

Even after switching to Japanese in GUI, some internal subsystems still run with English messages.
Ubuntu distributes language components modularly per language.
So only after installing language packs do we align the “internal language.”

Update Package Index First

Update repository information first.

sudo apt update

Ubuntu updates packages frequently.
Skipping this step can cause errors such as “language pack not found” or outdated versions being installed.

Install Japanese Language Packages

The two essential packages for Japanese localization are:

• language-pack-ja
• language-pack-gnome-ja (effectively required for GNOME users)

sudo apt install language-pack-ja language-pack-gnome-ja

*GNOME is Ubuntu’s default desktop environment
*On KDE or other desktops, a -kde-ja package may apply instead

Points to Check After Execution

After installation, Ubuntu switches internal message catalogs to Japanese.
Reflection requires a re-login.

You can verify by running:

locale

Expected output example:

LANG=ja_JP.UTF-8
LC_CTYPE="ja_JP.UTF-8"
LC_TIME="ja_JP.UTF-8"
...

If you still see some en_US.UTF-8 values,
the following sections (IME / fonts / locale adjustment) will resolve them.

Goal of This Step

• Unify internal OS message language to Japanese
• Align the “visual” GUI result with the internal command-line language

4. IME (Japanese Input: Mozc) Configuration

The Input Method Defines the “Feel” of Japanese Localization

Even if UI is Japanese, you cannot call it practical Japanese localization unless you can input Japanese text.
On Ubuntu, Mozc (based on Google Japanese Input) is the most stable and accurate IME in practice.

Here we install Mozc and ensure that “Hiragana input works properly.”

1) Install Mozc

Run this command in the terminal:

sudo apt install ibus-mozc

This one line installs Mozc itself and configures it with IBus (Ubuntu’s default input framework).

Ubuntu Desktop uses IBus as the default IME framework
KDE environments using Fcitx require different packages
(This article assumes Ubuntu Desktop default)

2) Add Mozc to Input Sources

1. Open Settings
2. Go to Region & Language
3. Click “+” under “Input Sources”
4. Select Japanese → Add “Mozc Japanese Input”
5. Place it below US keyboard (typical practical ordering)

Now the system is capable of switching into “Japanese Input.”

3) Re-login Is Often Required to Apply IME

A common mistake: Mozc is installed but conversion doesn’t work yet.
Because IME is a session-resident component, re-login is the safest way to activate it.

4) Confirmation — How to Verify Input

In a text editor or browser URL bar:

• Hankaku/Zenkaku key
• Super + Space (varies by environment)

If you can toggle between “あ｜A”, you are good.

5) Why Mozc Is Recommended

→ “usable Japanese input” out of the box.

5. Japanese Font Optimization

Japanese Fonts Affect Visual Comfort and Work Speed

With default Ubuntu installation, users often feel:

“spacing looks off” or “dotted accents look crushed.”

This is not just “lack of familiarity.”
The rendering is not optimized for Japanese fonts.
Especially when using bundled CJK fonts, glyph width/weight may not match Japanese expectations.

Recommended Font: Noto CJK

Developed jointly by Google and Adobe — highly compatible with Ubuntu.

Installation is extremely simple:

sudo apt install fonts-noto-cjk

This alone improves Japanese rendering system-wide.

Notable Improvements

• No crushed dotted accents
• Smoother glyph width for UI labels
• Stable display quality in LibreOffice and browsers

When to Add IPA Fonts

If you work with technical documents or vertical writing and prefer sharper text “tightness,” you may add the fonts-ipa family.

Example:

sudo apt install fonts-ipafont

However, for first-time setup Noto CJK alone is enough.
You can add more font families later based on your use case.

Order Between Fonts and IME

People sometimes ask: Should I install fonts before IME?
The conclusion:

Either order is fine for functionality.
But fonts have the fastest “visible impact.”

Once Japanese UI rendering stabilizes,
the feeling of “Ubuntu is now Japanese” increases dramatically —
so installing fonts early is psychologically beneficial.

6. Handling “Only Some Parts Remain English”

Typical Case: Only “That One App” Is Still English

Even when GUI is Japanese and Mozc works,
some apps still have English UI.

This does not mean that your configuration is wrong.
It is caused by apps being distributed using different packaging formats
or requiring individual language packs.

Common Cause #1: Snap / Flatpak Apps

Ubuntu nowadays frequently distributes apps as Snap.

Snap is a container-like package,
and may bundle language resources internally.

→ In such cases, “OS-level Japanese localization” and the app’s internal language setting are separate.

Solution

• Stop using Snap → use the deb edition
• If Flatpak version includes Japanese, switch to Flatpak

VSCode / Firefox often localize correctly just by switching:
Snap → deb.

Common Cause #2: Apps With Per-App Language Packs

Representative example: LibreOffice

LibreOffice requires a separate package:

sudo apt install libreoffice-l10n-ja

This alone replaces most UI strings with Japanese.

Common Cause #3: Locale Not Unified

GUI is Japanese, but terminal messages are still English → common phenomenon.

locale

If output is not ja_JP.UTF-8, adjustments are needed in later sections.

Decision Matrix

“Some English remains even though I localized properly” is normal.
Fixing these cases brings you to just before “complete.”

7. Common Pitfalls and How to Avoid Them

1) Not Re-logging / Not Rebooting

Language packs and IME operate “inside the session.”
Meaning — installation alone may not fully apply changes.

Guideline:

“Mozc doesn’t work → did not re-login” is extremely common.

2) Snap Edition of Firefox / VSCode Use Separate Handling

Firefox (Snap default since 2023)
VSCode (Ubuntu Software store = Snap)

These often require separate language handling.

Improvement examples:

• Firefox → deb edition
• VSCode → Microsoft official .deb

No need to “hate Snap” — but for Japanese UI, deb is quicker.

3) Locale Mismatch

GUI in Japanese but terminal errors still English → extremely common.

Check:

locale

Example:

LANG=ja_JP.UTF-8

If not — locale reset is required.
(This is covered later)

4) Not Installing Japanese Fonts, Leaving “Weird Feel”

Unstable Japanese UI appearance is often just because Noto CJK is not installed.

5) “Looks Japanese, But Formats Still US”

If Formats is not “Japan,” then:

• date
• decimal separator
• currency

— all follow non-Japan rules.

Language and Formats must always be set as a pair to “Japan.”

8. Summary

Japanese localization in Ubuntu is not “one setting and done.”

UI → language packs → IME → fonts → per-app → locale

— this is a layered sequence.

But conversely:

• Don’t skip re-login
• Snap apps need separate consideration
• Use Noto CJK fonts

Just following these three points
eliminates most “Japanese localization pain.”

Once familiar, the entire workflow takes about 30 minutes.
With minor tuning, Ubuntu becomes an excellent platform for productive Japanese-language creation.

9. FAQ

Q. GUI is in Japanese, but terminal messages are still English.

A. Locale is likely not unified.
Check ja_JP.UTF-8 via locale.

Q. I installed Mozc but cannot type Japanese.

A. Did you add Mozc to input sources?
If yes, re-login.

Q. Only LibreOffice is English — what should I do?

A. Install libreoffice-l10n-ja.

Q. Are fonts mandatory?

A. “Not mandatory but high impact.”
They improve clarity and readability.

Q. Are Snap apps harder to localize?

A. Often “yes.”
Switching to deb editions usually solves it faster.