Firefox just got better for Chinese, Japanese and Korean speakers on Android

When Firefox users ask for better translation support, we make it happen.

Thanks to your feedback on Mozilla Connect, Firefox now supports Chinese, Japanese, and Korean (often referred to as CJK) translation, both on desktop and Android. That means millions more people can browse and translate the web in their language, without sending their content to the cloud.

We saw so many requests on Mozilla Connect for CJK support," said Marco Castelluccio, engineering manager. It was clear. This is what users wanted us to prioritize."

Translation without tracking

Unlike other browsers that send your content to the cloud for translation, Firefox handles everything locally on your device. That means more privacy, more control, and it even works offline once the language model is downloaded.

Firefox automatically downloads the model once," explained Erik Nordin, software engineer. After that, translations happen on your phone. The content never leaves your device, and Firefox does not track what you translate."

On-device translation requires efficiency. Mobile devices have limited memory and processing power, so the team developed smarter translation algorithms that prioritize the content you're actually reading.

If you're only reading the top of a long page, Firefox won't waste time and energy translating the whole thing," Erik said.

This approach is part of Mozilla's broader mission to build technologies that respect your privacy by design. No compromises.

We took our time to get it right

Chinese, Japanese and Korean use characters, grammar and sentence structures that vary significantly from Latin-based languages.

Our earlier translation algorithms were not able to handle writing scripts that do not insert a space character between sentences," Erik said. CJK languages required us to rethink both the architecture and how we algorithmically segment text."

And there's simply less open-source data available to train CJK translation models compared to European languages.

Our models are trained completely on publicly available data," said Marco. That's important for transparency, but it also means it's harder to find enough good-quality examples for CJK languages."

To make things even trickier, Firefox translation works locally. That means the models had to be smart enough to handle these complex languages and lightweight enough to run on mobile phones.

We had to rework our algorithms to make translation feel faster and more responsive," Erik said. Now, Firefox prioritizes the part of the page you're looking at instead of translating everything at once."

To overcome these challenges, the team upgraded their machine learning models, overhauled the sentence segmentation pipeline, and optimized performance to ensure a smooth experience - especially on older and low-end Android devices.

What stuffed mushrooms taught us about machine learning

Mozilla engineers don't speak every language we support. That's why we leaned on the community and our collegues to help test CJK translation before launch. Volunteers tried out early versions in Firefox Nightly and flagged issues.

That feedback was gold," Erik said. It helped us tweak the models and make sure the translations made sense in real-world use."

And it was essential. Neither Marco nor Erik speaks any of the CJK languages. (Marco speaks Italian and English, and Erik is fluent in English with conversational Spanish.) To validate accuracy, they relied on community testers, Mozillians fluent in Chinese, Japanese or Korean, and members of MozAPI, Mozilla's resource group for Asian and Pacific Islander employees.

One tester pointed out a restaurant menu item translating stuffed mushrooms' as a plush toy," Erik laughed. It was a great reminder of how nuanced language can be."

We can measure accuracy with automated tools," Erik added, but there's no substitute for a native speaker saying, Yeah, that sounds right,' or Actually, this reads a little strange.'"

Try Chinese, Japanese and Korean translation now built into Firefox

CJK translation is already making a difference. Since launching support on desktop, Firefox has more than doubled active translation users in Asia. With Android support now rolling out in Firefox, even more people can experience the web in their language, safely and privately.

Update to the latest version of Firefox for Android or desktop to start using CJK translation. Then, tap the translate icon when you visit a page in Chinese, Japanese or Korean. Firefox will do the rest, right on your device. For a list of all the translations available on Firefox, visit here.

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