From Forge Community Wiki

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, block.minecraft.dirt 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 en_us. A list of available locales can be found on the Minecraft Wiki.


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 registry names instead.

Language files

Language files are located by assets/[namespace]/lang/[locale].json (e.g. the US English translation for examplemod would be assets/examplemod/lang/en_us.json). The file format is simply a json map from translation keys to values. The file must be encoded in UTF-8.

  "item.examplemod.example_item": "Example Item Name",
  "block.examplemod.example_block": "Example Block Name",
  "commands.examplemod.example_command.error": "Example Command Errored!"

Usage with Blocks and Items

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 getDescriptionId(). Item also has getDescriptionId(ItemStack) which can be overridden to provide different translation keys depending on ItemStack NBT.

By default, getDescriptionId() will return block or item. prepended to the registry name of the block or item, with the colon replaced by a dot. BlockItems will take their corresponding Block's translation key by default. For example, an item with ID examplemod:example_item effectively requires the following line in a language file:

  "item.examplemod.example_item": "Example Item Name"

Localization methods


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.

To respect the language settings of clients, the server should have clients localize text in their own locale using components with TranslatableContents or other methods preserving the language neutral translation keys.



This I18n class can only be found on the 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.

get(String, Object...) localizes in the client’s locale with formatting. The first parameter is a translation key, and the rest are formatting arguments for String.format(String, Object...).


TranslatableContents is a ComponentContents 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 TranslatableContents(String, Object...) constructor is a translation key, and the rest are used for formatting. The only supported format specifiers are %s and %1$s, %2$s, %3$s etc. Formatting arguments may be other Components that will be inserted into the resulting formatted text with all their attributes preserved.

A MutableComponent can be created using Component#translatable by passing in the TranslatableContents's parameters. It can also be created using MutableComponent#create by passing in the ComponentContents itself.