How Mercari is taking Japan’s largest marketplace to the world
Mercari is one of Japan’s most ambitious technology companies. With around 23 million monthly users, a public listing, and a growing portfolio spanning C2C commerce, mobile payments, and crypto assets, the company is pursuing its boldest move yet. It is transforming a domestic marketplace into a cross-border commerce platform, already live in Taiwan, Hong Kong, and the US, with plans to expand further. To move at the speed the business demands, a small team adopted AI across its global content operations through the Phrase Platform. Product language coverage grew by 250% and translation speed increased by 18%, all without adding headcount. The result is an infrastructure that scales with the business.
Mercari is a publicly traded Japanese technology company (TSE 4385) with more than 2,000 employees from over 50 countries working out of its Tokyo headquarters. Founded in 2013, it operates Japan’s largest C2C marketplace, a US subsidiary, and a growing cross-border commerce platform. Mercari’s portfolio also spans mobile payments, crypto assets, and mobile telecommunications. The company’s mission is to circulate all forms of value to unleash the potential in all people.
The company’s international strategy centers on its global app, which allows customers outside Japan to purchase items directly from Japanese sellers and have them shipped cross-border. As Mercari expands into new markets, every customer touchpoint needs to work in the local language, from the product interface to corporate communications, investor materials, and media relations.
CHALLENGE
A small team with a global remit
As Mercari evolved from a domestic marketplace into a cross-border commerce platform, operational demands grew far faster than the team itself. Every new market and every product release requires content that represents the Mercari brand consistently and accurately, and the volume was becoming unmanageable.
On the product side, there was no centralized record of the content requiring adaptation for new markets. Supporting additional languages in the global app meant spending weeks identifying what already existed before work could begin.
On the corporate side, the quality of machine-generated content was not fit for purpose. The output often required complete retranslation rather than review, effectively doubling the cost of every piece of content as well as slowing the process. As the business expanded internationally, the volume of content required became increasingly difficult for the team to manage at scale.
“Without a centralized system, there was no way to see what strings existed or what translation values were in place. Anyone who needed that visibility had to go through engineers, creating unnecessary dependencies and delays just to answer basic questions. Phrase made the content landscape visible and manageable for everyone.”
SoonHyung Kwon Product Manager, Mercari
SOLUTION
Two jobs, one platform, and AI that earns its place
In 2025, Mercari announced a company-wide move toward becoming AI-native, pushing every function to integrate AI into its operations. Having used Phrase for several years, the team began exploring how the Phrase Platform could support that ambition. For the teams responsible for the product and global communications, this became an opportunity to fundamentally rethink how they work.
The response played out in two ways.
For product UI, the team needed a way to manage content across a rapidly growing number of markets without relying on engineers to manually track and update strings in the codebase. Phrase Strings provided a centralized platform that could scale with the business. PProduct Manager Soon Hyung Kwon and his team integrated Phrase Strings with the existing design and development toolchain. They also configured Phrase Language AI to generate first-pass translations for production releases, with regular agency reviews to maintain quality.
For corporate content, Emma Davis, Translator, led the evaluation of multiple AI engines, testing Phrase Next GenMT, Phrase Custom AI, and external tools. The focus was on both accuracy and speed, because the two are inseparable in practice. Poor output quality meant more time spent rewriting, which eliminates any speed advantage. With Phrase Next GenMT the internal team increased translation speed by 18%. Phrase’s flexibility in supporting an AI/ML data training opt-out amendment also reinforced the team’s confidence in the platform’s governance approach.
Mercari’s implementation of the Phrase Platform now supports multiple parts of the business through a connected AI-powered content workflow.
Faster product releases.Phrase Strings replaced a fragmented approach to product content with a single centralized platform. New designs flow directly through the Figma plugin, developers connect through the API, and new features and languages are all handled through one system without manual handoffs. Product updates now launch simultaneously across all supported languages, and adding a new market no longer requires weeks of engineering support.
Corporate content that keeps pace with the business. Phrase TMS translates and localizes blog posts, press releases, and investor communications as well as internal comms to support Mercari’s international workforce. Phrase Next GenMT generates a first draft that the team refines and reviews. Content that previously could not be produced at all due to capacity constraints is now part of the regular pipeline.
AI that was tested, not assumed. Phrase Next GenMT via Phrase Language AI serves as the default engine across both workstreams, selected after Mercari’s comprehensive evaluation. It was chosen because it delivered the greatest efficiency gains inside the team’s production workflow, where speed and integration mattered as much as raw output quality.
A corporate voice that sounds human. Auto Adapt enables the team to iteratively refine AI output for customer-facing blog posts where natural, human-sounding language matters most. Standard machine translation has historically struggled to deliver the quality required. By producing output that already reflects how Mercari communicates, Auto Adapt eliminates much of the manual post-editing that previously slowed the team down. It captures the brand voice in a way that generic machine translation had never achieved and continues improving as the voice evolves.
“We needed this urgently. We didn’t have time to run a lengthy evaluation across multiple vendors. We already had a relationship with Phrase, and when we tested the engines against our actual workflow, the results confirmed we’d made the right call.”
SoonHyung Kwon Product Manager, Mercari
“We already trust Phrase with sensitive and confidential data. When it came to choosing between Phrase and standalone AI tools, the decision was clear. We needed that level of governance to move forward.”
Emma Davis Translator, Mercari
STATS & FACTS
The numbers behind the transformation
250%
Increase in product language coverage
18%
Faster translation speed through AI-assisted workflows
0
Additional headcount required despite expanding to five new product languages
75%
Reduction in engineering time per platform when adding a new product language with Phrase Strings
“It’s hard to imagine how we would work without Phrase. I’ve been at Mercari since before we had it. At the time, that felt fine. But having seen what’s possible now, there’s no going back.”
Emma Davis Translator, Mercari
WHY PHRASE
Trust, governance, and a platform that could grow with the business
Prior to Phrase, content was managed without a centralized system. Mercari chose the Phrase Platform to solve that fundamental operational problem, and the platform became the foundation for everything that followed.
As new demands emerged across the business, Mercari continued building on the Phrase Platform. The product team chose Phrase Strings because the platform was already proven and trusted, and consolidating onto a single vendor reduced both cost and complexity. For AI, the decision came down to governance. Mercari’s data handling and security requirements are rigorous, and Phrase had already cleared those hurdles. When the team evaluated standalone AI tools against Phrase’s integrated capabilities, the trust that had been built over years of working together made the choice straightforward.
THE IMPACT
More markets, more content, same team
The most visible change is speed to market. Phrase has made the product content landscape visible and manageable, giving teams a centralized way to manage strings, reduce engineering dependencies, and coordinate multilingual releases across supported languages.The most visible change is speed to market. Now it is an operational decision rather than a major project. Feature releases go live simultaneously across all supported languages. With Phrase centralizing strings across platforms, teams can reduce cognitive load, improve consistency, and apply updates from one place. This enables the infrastructure to scale without proportional increases in cost or headcount.
For Mercari’s customers, the change is felt directly. Buyers in Taiwan and Hong Kong can now browse, purchase, and receive support in their own language from day one. New product features can reach every market at the same time with all the languages prepared simultaneously. As Mercari enters additional markets, customers will experience a fully localized product from launch, which builds trust and reduces friction at the point where it matters most.
On the corporate side, the team went from turning away content requests to actively expanding its coverage. Blog posts, press releases, and investor materials that previously went unproduced are now part of the regular output, strengthening Mercari’s global brand presence without the need for additional resources.
The impact is now extending beyond the original team. Other product groups within Mercari have adopted Phrase Strings for their own content, recognizing growing international demand within the domestic Japanese marketplace itself as the company’s workforce becomes more globally diverse.
“Every time we release a new feature, it needs to work in every language. Engineers used to manage that manually. Now they focus on the source language, and Phrase Strings handles the rest. That alone has changed the speed at which we can move.“
SoonHyung Kwon Product Manager, Mercari
LOOKING AHEAD
Next stop, the rest of the world
Mercari’s expansion plans continue to accelerate. The global cross-border commerce app is now live in the US, with additional markets and languages to follow. Every new market reinforces the value of the infrastructure the team has built.
As AI quality continues to improve, the ambition is to expand both the breadth and volume of content the team can produce while maintaining the brand voice that Mercari’s global customers expect.
For a company whose mission is to circulate all forms of value to unleash the potential in all people, building a product and brand that work across markets is central to Mercari’s global ambition.
The direction Phrase is heading with AI-native features makes complete sense for where Mercari is going. We’re building for global scale, and we need a platform that’s doing the same.
SoonHyung Kwon
Product Manager
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