New returns a new Catalog.

String specifies a plain message string.

Var sets a variable that may be substituted in formatting patterns using named substitution of the form "${name}".

ErrNotFound indicates there was no message for the given key.

A Catalog holds translations for messages for supported languages.

A Context is used for evaluating Messages.

A Message holds a collection of translations for the same phrase that may vary based on the values of substitution arguments.

An Option configures Catalog behavior.