Catalogs

A catalog is a structured collection of the extracted messages. First, as soon as the messages are extracted, they are put in the .po files. And for use within the application after translation, they are compiled into compiled catalogs.

There is one .po file per locale.

.po files

This is the primary catalog format of the messages. It contains some headers with some metadata and the plural rule for the language, the untranslated messages as message IDs and the translations. A simple example of the contents, before translation is this:

es.po

# ...other headers
"Plural-Forms: nplurals=2; plural=n == 1 ? 0 : 1;\n"

#: src/path/to/source1.svelte
msgid "Hello world!"
msgstr ""

#: src/path/to/source2.svelte
msgid "Welcome"
msgstr ""

Then it is edited by the translator (or Gemini) to also have the translation like this:

es.po

# ...other headers
"Plural-Forms: nplurals=2; plural=n == 1 ? 0 : 1;\n"

#: src/path/to/source1.svelte
msgid "Hello world!"
msgstr "¡Hola Mundo!"

#: src/path/to/source2.svelte
msgid "Welcome"
msgstr "Bienvenido"

But this is not what is loaded by the application, it is only for storage and exchange with translators. To be used in the application, it gets compiled into:

Compiled catalogs

Compiled catalogs are JavaScript modules that contain only the necessary information. And depending on the configuration, they can be virtual modules (default) or written to disk. The above example catalog, after compilation becomes:

es.compiled.main.js

export const c = ["¡Hola Mundo!", "Bienvenido"]
export const p = n => n == 1 ? 0 : 1

That’s all. No keys, no unnecessary data. During development there is HMR related code added but not for production.

Depending on the configuration, there can be one compiled catalog per .po file, or more. If granularLoad is enabled, for example, the above single .po file will become two compiled catalogs per the source file (source1.svelte and source2.svelte)

es.compiled.src_path_to_source1_svelte.js

export const c = ["¡Hola Mundo!"]
export const p = n => n == 1 ? 0 : 1

es.compiled.src_path_to_source2_svelte.js

export const c = ["Bienvenido"]
export const p = n => n == 1 ? 0 : 1

This may be desired to reduce the bundle size when each page hash a huge number of messages.

loadID

When using the default configuration, there is only one compiled catalog per locale for one adapter. But when using granularLoad, then the compiled catalog is broken into smaller parts. This necesitates a way to refer to those different parts when loading them. This identifier is called a loadID.

When not using granularLoad there is only one loadID and it is the same as the adapter key. (E.g. main).

But when using granularLoad, a loadID is generated from each file name, using the generateLoadID function. That function can return unique identifiers to have separate compiled catalogs per file, or it can selectively return the same identifiers for multiple file names to make them share the same compiled catalogs.