# Localization

> Translate an app's messages and follow the language it shows.

## Messages

`locales/` beside `nsgo.yaml` holds the app's messages, a YAML file per language (`en.yaml`, `de.yaml`) in ICU MessageFormat:

```yaml
greeting: Hello, {name}!
appName:
  message: Hello
  description: The app's name, for translators.
```

A message is a string, or `message` with a `description` and `placeholders` for translators.

The package imports `locales/`. `dev`, `build` and `test` check the catalogs and write a Go function per message beside them, such as `locales.Greeting(cx, "Ada")`, which says it in the language the app shows and follows it as it changes; `go tool nsgo i18n` writes the functions alone. Messages format numbers and dates (`{d, date, medium}`), and `appName` names the app in each language in its packages.

## The language

`cx.SetLocale("de")` chooses the language, and the layout runs in the direction it is written in.

```sh
go tool nsgo dev -lang en-XA
```

runs the app in a pseudo locale that shows untranslated and cut text. Any build takes it as it starts: `--nsgo-lang=en-XA`.

## Weeks, times and measures

`i18n.Regional(cx)` says how the user reads weeks, times and measures, apart from the language: the day weeks start on, 12- or 24-hour time and the measurement system, as they set them on the platform, else as their region does. Calendars and date pickers start their weeks there and time fields show those hours unless the app sets `FirstDayOfWeek` or `HourCycle`, and the times a catalog's messages write follow the user's hours.

## NSGo's own words

NSGo's components say their words in the languages NSGo is translated to. For another language, a key that names a package, such as `github.com/nsgo-dev/nsgo/base/locales`, gives that package's messages in the file's language.