The interface will immediately switch to English.

Many users confuse system language with typing language. You can easily type in any language using the Google Keyboard (Gboard).

How to add a full keyboard language:

This works 100% for any language. You can type emails, SMS, and chats in any script, even if the phone menus are in Japanese or English.

Even if English is successfully enabled, the user experience on the Fujitsu F-04J remains distinctly Japanese.

Before you start tapping blindly through menus, it is crucial to manage expectations.

The Fujitsu F-04J runs Android 7.1.1 Nougat (or later, depending on updates). Android, by nature, supports dozens of languages. However, docomo (the carrier) and Fujitsu often restrict the visible list to Japanese only. Do not panic. The language files for English (US/UK), Chinese, and often Korean are still present on the phone. You just need to access them.

Confirmed supported languages on F-04J:

Note: European languages like French, German, or Italian are generally NOT available on Japanese domestic models.

Use Settings search:

The F‑04J features a 5‑inch display, water resistance, and docomo’s proprietary UX interface. By default, the system language is set to Japanese. Users outside Japan may wish to switch to English or another language. However, docomo firmware restricts the language list more than standard Android.

This is the core of the process. Since your menu is likely in Japanese, follow these steps by icon recognition rather than reading text.