The Translate Button Is Declarative; the Community Workflow Is Not

The translate button in a multilingual community chat application may appear to solve language barriers, but the underlying workflow presents complex challenges. When a user requests translation, the system must record the request, handle failures, manage changes to the original message, and allow moderators to review the translation. The translation process itself is an imperative operation, distinct from the declarative nature of the user interface.

The tutorial demonstrates how to build a workflow around Tencent RTC's translation capability for a social messaging experience. The design adheres to six rules: recording translation requests, rejecting locally without invoking translation if the source is not eligible, handling translation failures by keeping the original message visible, discarding late results when the source changes, preserving machine translations and opening human review for disputed meanings, and labeling corrections as human corrections instead of rewriting history.

The architecture consists of an event-driven pipeline, where user commands are processed by pure decision functions, append domain events, and trigger imperative workers. Pure code determines the validity of requests and the UI display, while the imperative shell deals with operations that can fail, such as persisting events, invoking translation, and notifying moderators. This separation of pure and imperative code highlights where nondeterminism enters the system, making it clear where engineering judgment is needed.