'''Internationalization''' (shortened as '''i18n'''), is a way of designing code so that it requires no changes to be adapted for various languages. '''Localization''' (shortened as '''l10n''') is the process of adapting displayed text to the user’s language.
Internationalization is implemented using ''translation keys''. A translation key is a string that identifies a piece of displayable text in no specific language. For example, <code>block.minecraft.dirt</code> is the translation key referring to the name of the Dirt block. This way, displayable text may be referenced with no concern for a specific language. The code requires no changes to be adapted in a new language.
Localization will happen in the game’s locale. In a Minecraft client the locale is specified by the language settings. On a dedicated server, the only supported locale is <code>en_us</code>. A list of available locales can be found on the [https://minecraft.gamepedia.com/Language#Available_languages Minecraft Wiki].
{{Tip/Important|The only purpose of a translation key is internationalization. Do not use them for logic, such as comparing if two blocks are equal. Use their [[Registration/1.18|registry names]] instead.}}
== Language files ==
Language files are located by <code>assets/[namespace]/lang/[locale].json</code> (e.g. the US English translation for <code>examplemod</code> would be <code>assets/examplemod/lang/en_us.json</code>). The file format is simply a json map from translation keys to values. The file must be encoded in UTF-8.
Block, Item, and a few other Minecraft classes have built-in translation keys used to display their names. These translation keys are specified by overriding <code>getDescriptionId()</code>. Item also has <code>getDescriptionId(ItemStack)</code> which can be overridden to provide different translation keys depending on <code>ItemStack</code> NBT.
By default, <code>getDescriptionId()</code> will return <code>block</code> or <code>item</code>. prepended to the registry name of the block or item, with the colon replaced by a dot. <code>BlockItem</code>s will take their corresponding Block's translation key by default. For example, an item with ID <code>examplemod:example_item</code> effectively requires the following line in a language file:
{{Tip/Important|A common issue is having the server localize for clients. The server can only localize in its own locale, which does not necessarily match the locale of connected clients.
<br/><br/>
To respect the language settings of clients, the server should have clients localize text in their own locale using <code>TranslatableComponent</code> or other methods preserving the language neutral translation keys.}}
{{Tip/Danger|'''This I18n class can only be found on the [[Sides#Different Kinds of Sides/1.18|physical client]]!''' It is intended to be used by code that only runs on the client. Attempts to use this on a server will throw exceptions and crash.}}
<code>get(String, Object...)</code> localizes in the client’s locale with formatting. The first parameter is a translation key, and the rest are formatting arguments for <code>String.format(String, Object...)</code>.
<code>TranslatableComponent</code> is a <code>Component</code> that is localized and formatted lazily. It is very useful when sending messages to players because it will be automatically localized in their own locale.
The first parameter of the <code>TranslatableComponent(String, Object...)</code> constructor is a translation key, and the rest are used for formatting. The only supported format specifiers are <code>%s</code> and <code>%1$s</code>, <code>%2$s</code>, <code>%3$s</code> etc. Formatting arguments may be other <code>Component</code>s that will be inserted into the resulting formatted text with all their attributes preserved.