Message Translation

The first functionality that Fuchsia's localization provides is message translation. Conceptually this gives a program the ability to display user-facing messages in the user's language of choice. This is achieved using locale-sensitive formatter printing. The program needs to keep the "localization context" where user's localization preferences are stored. When, in the course of program execution, there comes a point that a message "Hello world!" needs to be displayed on screen in the user's native language (for example Spanish would be encoded as "es", for European Spanish, and "es-419" for Spanish as used in the Americas), the program can look up a translation by providing an abstract [Lookup] service with the original message and the desired translation. Conceptually this will amount to a line in the code that matches this general pattern:

[Lookup].String({locale-ids=["es-419"]}, MSG_Hello_World) ⇒ (yields the translation)

In the above example, [Lookup] can be any sort of callable endpoint: it could be a library exposed function, or could be an interface point for an RPC stub that fetches the translation over the network. The abstract operation of "fetching a translated message" is here called String to distinguish it from other possible calls to typed data, such as StringArray or others.

Note, messages can get quite a bit more elaborate than that, which is why we typically don't want the program authors to handle them directly, but rather through message IDs.

Two more things are of note:

  1. The language identifiers are specified as Unicode locale IDs (hence the named parameter locale-ids in the example), and multiple such locale IDs can be provided at once. This is because users may have more than a single preferred language, and may have a hierarchy of languages by preference. This allows the localization system to choose the best available message, possibly in more than a single language in a single session.
  2. The messages are not specified as their string representation in code. Rather, they are referred to by a unique message identifier. In the example above, this was arbitrarily named MSG_Hello_World. While schools of thought differ on whether strings should be internalized or externalized, we opted for the latter. Our main reasons were to keep the source code free from linguistic concerns, which makes the translation toolchain somewhat easier to maintain, and makes translations at scale easier to manage.

Two main questions arise from the example above:

  1. What does the concrete interface to the [Lookup] service look like in the programmer's language of choice? And,
  2. How do translations make their way to my program so that they are available to use?

We will answer these in turn when we talk about the Lookup API.