The English Translation
In Fluent, most messages are simple text strings identified by an identifier. In the first message in the example, tabs-close-button is the identifier and Close is the value.
Sometimes, translations require a little bit of logic to sound right in the target language. In the tabs-close-tooltip message, the correct variant of the translation depends on the value of the $tabCount variable. The names of the variants, [one] and [other] , are standard names of the plural categories defined by the Unicode in CLDR.
On the other hand, when no logic is required, translations in Fluent stay simple. The tabs-close-warning message appears in Firefox when the user tries to close a window with more than one tab. The message is only displayed when the tab count is 2 or more, and so in English, the word tab will always appear as the plural tabs.
-sync-brand-name is a special kind of message in Fluent, called a term. Term identifiers always start with a dash. Terms can be referenced by other messages, but cannot be displayed directly in the app. Referencing terms is a powerful tool for ensuring consistency. Once defined, a translation can be reused in other translations.