Scoped context

[Myzel394]

Problem Description

When using lingui purely server side (no React), globally setting the language can easily lead to race issues. Example:

// First this request is executed
http.get("/", () => {
  i18n.activate("cz");

  // Second, a long running request, now another request occurs (see below)
  someLongRunningTask();

  // Fifth, this should be Czech, but it is Spanish now
  return t`Welcome`;
})

// Third, this request is executed
http.get("/hola", () => {
  // Fourth, language changed to es
  i18n.activate("es");

  return t`Hello`;
})

Proposed Solution

Introduce the possibility to scope a language. For example:

i18n.scope({
  language: "cz",
}, ({t}) => {
  return t`Welcome` // <- this `t` is now scoped to Czech and won't change.
})

Alternatives Considered

Add a locale option to the translation functions such as t, msg, etc.

Additional Context

No response

[timofei-iatsenko]

TL;DR;
Use NodeJs's AsyncLocalSorage + runtimeConfigModule.

Explanation:

• Create a custom module with custom i18n instance. Basically this instance would just retrieve current AsyncLocalSorage context and getting an instance from there and redirect a call to that instance.
• Set runtimeConfigModule to use your i18n instance instead of default from @lingui/core
• Wrap the place where your requests is handled (say in the express handler) with this AsyncLocalStorage call

This will allow you to still use a global t macro without worrying about polluting other user request.

Unfortunately this couldn't be incorporated to a library because the variety of the way how the backend might be configured, what framework you use, what runtime you use etc so big so Lingui simply couldn't cover every possible case.