Design Cross-Server Real-Time Chat Translation for Roblox Players
Company: Roblox
Role: Product Manager
Category: System Design
Difficulty: medium
Interview Round: Other
Roblox players speak many languages, and the company already has a machine learning model that can translate text. Design the system that uses it so players connected to different servers can chat with one another automatically, each reading messages in their own language.
```hint Follow one message
Trace a single chat line from the sender to recipients on other servers who read different languages. Ask at which step you know which languages are needed, and how many times the same text would reach the model if every recipient were handled separately.
```
### Clarifying Questions
- Does "different servers" mean separate game server instances of the same experience, chats that span experiences such as friend messages and group chats, or both?
- Is the translation model available as a service we call per message, and do we know its latency and cost per call, or must this design also host and scale it?
- Is this text chat only, or should voice chat be translated too?
- Must every translated message pass the same safety filtering as the original, and which age-based chat settings does the design have to respect?
### What a Strong Answer Covers
- How a message travels from the sender to recipients on other servers, and the point where its source language is detected and the needed target languages are known.
- How translation stays fast enough for live chat and affordable at Roblox's scale, including reuse of work across recipients and servers.
- Safety: how translated text is filtered, and how the design keeps translation from becoming a way around moderation.
- Behavior when translation is slow, wrong or unavailable, and how quality is measured per language pair.
- Product metrics showing that players communicate more across languages, with guardrails for safety, latency and cost.
### Follow-up Questions
- Players reading one language pair keep tapping to see the original message. How do you find out why, and what do you change?
- A popular experience has its own slang and item names that the model keeps mistranslating. How should the system handle terms the model does not know?
- How would the design change if Roblox also wanted to translate voice chat?
Overview: A Roblox product manager system design question about building the service that applies an existing machine learning translation model so players on different game servers can chat in their own languages. It tests message flow across servers, latency and cost at scale, safety filtering of translated text, failure handling and success metrics.