# Internationalization

## The `lang` route parameter

All page paths starts with a language parameter, e.g. `/sv/utforska-scandic/wi-fi`.

### Get the language in a client component

We have a hook called `useLang` that directly returns the `lang` parameter from the path.

### Get the language in a server component

In order to not prop drill that all the way from a page we use React's `cache` in a way that resembles React`s context, but on the server side.

For this to work we must set the language with `setLang` on the topmost layout

This was inspired by [server-only-context](https://github.com/manvalls/server-only-context)

## Translations a.k.a. UI labels a.k.a. Lokalise

### Quickstart: How to use react-intl in the codebase

> For more information read about [the workflow below](#markdown-header-the-workflow).

- **Do not destructure `formatMessage` from either `getIntl()` or `useIntl()`.**

  ❌ Do not do this:

  ```typescript
  const { formatMessage } = useIntl()
  const message = formatMessage(...)
  ```

  ✅ instead do this:

  ```typescript
  const intl = useIntl()
  const message = intl.formatMessage(...)
  ```

  ❌ Do not do this:

  ```typescript
  const { formatMessage } = await getIntl()
  const message = formatMessage(...)
  ```

  ✅ instead do this:

  ```typescript
  const intl = await getIntl()
  const message = intl.formatMessage(...)
  ```

- **Do not pass variables as defaultMessage.**

  The `defaultMessage` needs to be a literal string so that the tooling can properly find and extract defined messages. Do not use template strings with variable interpolation either.

  ❌ Do not do this:

  ```typescript
  const data = await getSomeData()
  ...
  const message = intl.formatMessage({
    defaultMessage: data.type,
  })
  ...
  const message = intl.formatMessage({
    defaultMessage: `Certification: ${data.type}`,
  })
  ```

  ✅ instead do this:

  This is a hard one to give a general solution/rule for, but in essence it should use either use a "switch approach" or `defineMessage/defineMessages` ([docs](https://formatjs.github.io/docs/react-intl/api/#definemessagesdefinemessage)) in some way.

  The most common reason for this scenario is that the data contains one or several words/sentences we want translated.

  The preferred solution is to use a "switch approach" (or something equivalent), checking some property of the entity to decide what message to use.

  - It is explicit about what cases are supported: this helps finding bugs by lowering complexity by making it easier to find where a string is used.
  - The declaration is coupled with the usage: keeping our messages up to date and clutter free over time.
  - The formatjs eslint plugin helps enforce proper usage.
  - TypeScript will force us to keep the list up to date with the typings of `data.type`. Preferably ALL data points of this manner should be an enum or an array of strings `as const` (or equivalent) for the best TS support here.

  ```typescript
  ...
  const data = await getSomeData()
  ...
  let message = intl.formatMessage({defaultMessage: 'N/A'})) // or some other default/"no match" message
  switch (data.type) {
    case "Restaurant":
      message = intl.formatMessage({defaultMessage: "Restaurant"})
      break;
    case "Bar":
      message = intl.formatMessage({defaultMessage: "Bar"})
      break;
    case "Pool":
      message = intl.formatMessage({defaultMessage: "Pool"})
      break;
    case "Some certification":
      message = intl.formatMessage({defaultMessage: "Certification: {name}"}, { name: "Some certification"})
      break;
    default:
      // TS will throw if it reaches here if typings for `data.type` are properly defined and the above cases are exhaustive.
      // This will help us keep messages up to date.
      const type: never = data.type
      console.warn(`Unsupported type given: ${type}`)
  }
  ```

  If the above is not possible the escape hatch is using something like the following. Avoid using this because:

  - This decouples the message declaration from the message consumption: causing stale messages to linger around and clutter up the codebase.
  - It makes it a lot harder to find where a string is being used in the codebase.
  - The formatjs eslint plugin is unable to enforce placeholders: this decreases confidence in our messages and potentially hiding bugs.

  ```typescript
  import { defineMessages } from "react-intl"
  ...
  const data = await getSomeData()
  ...
  const restaurantMessage = defineMessage({
    defaultMessage: "Restaurant",
  })
  const barMessage = defineMessage({
    defaultMessage: "Bar",
  })
  const poolMessage = defineMessage({
    defaultMessage: "Pool",
  })
  // OR
  const messages = defineMessages({
    restaurant: {
      defaultMessage: "Restaurant",
    },
    bar: {
      defaultMessage: "Bar",
    },
    pool: {
      defaultMessage: "Pool",
    }
  })
  ...
  return (
    <p>{intl.formatMessage(messages.restaurant)}</p> // or .bar or .pool, etc.
  )
  ...

  // Since calls to defineMessage/defineMessages get their messages extracted,
  // technically you can do the following instead of accessing the key like above.
  // But it is not encouraged as this decoupling leads to had to track usage and decay over time:
  const message = intl.formatMessage({
    // eslint-disable-next-line formatjs/enforce-default-message
    defaultMessage: data.type, // data.type === "Restaurant" | "Bar" | "Pool"
  })
  ```

- **Do not use defaultMessage key as an alias.**

  The `defaultMessage` should be the actual message you want to display (and send to Lokalise). It must be written in American/US English.

  ❌ Do not do this:

  ```typescript
  const message = intl.formatMessage({
    defaultMessage: "some.alias",
  })
  ```

  ✅ instead do this:

  ```typescript
  const message = intl.formatMessage({
    defaultMessage: "The real message is here in US English",
  })
  ```

- **Do not use conditionals when defining messages.**

  ❌ Do not do this:

  ```typescript
  const message = intl.formatMessage({
    defaultMessage: someVariable ? "Variable is truthy" : "Variables i falsey",
  })
  ```

  ✅ instead do this:

  ```typescript
  const truthyMessage = intl.formatMessage({
    defaultMessage: "Variable is truthy",
  })
  const falseyMessage = intl.formatMessage({
    defaultMessage: "Variable is falsey",
  })
  const message = someVariable ? truthyMessage : falseyMessage
  ```

- **Avoid using ICU special words as placeholder names**

  Some words have meaning in ICU when dealing with placeholders and such. To avoid bugs and confusion do not use them as placehodler names.

  Avoid (list is not exhaustive):

  - `{number}`
  - `{integer}`
  - `{plural}`
  - `{date}`
  - `{time}`
  - `{select}`
  - `{choice}`
  - `{other}`

  Also do not use the current variable name in scope as the placeholder name (unless the variable is named following the below rules). It will confuse translators.

  ❌ Do not do this:

  ```typescript
  const number = getValueSomeWay()
  ...
  const message = intl.formatMessage(
    {
      defaultMessage: "The number is {number}",
    },
    {
      number,
    }
  )
  ```

  nor this

  ```typescript
  const goodNameForVarButNotForPlaceholder = getValueSomeWay()
  ...
  const message = intl.formatMessage({
    defaultMessage: "The number is {goodNameForVarButNotForPlaceholder}",
  }, {
    goodNameForVarButNotForPlaceholder
  })
  ```

  ✅ instead do this:

  Prefer a placeholder name that gives context to the message when reading it without the context of the code

  ```typescript
  const goodNameForVarButNotForPlaceholder = getValueSomeWay()
  ...
  const message = intl.formatMessage(
    {
      defaultMessage: "The number is {membershipNumber}",
    },
    {
      membershipNumber: goodNameForVarButNotForPlaceholder,
    }
  )
  ```

  or if context is hard to give, use generic words like `value`, `count`, `amount`, etc.

  ```typescript
  const number = getValueSomeWay()
  ...
  const message = intl.formatMessage(
    {
      defaultMessage: "The number is {value}",
    },
    {
      value: number,
    }
  )
  ```

- Do not give id to messages.

  The eslint plugin will automatically fix this (removes the id on save/fix).

  ❌ Do not do this:

  ```typescript
  const message = intl.formatMessage({
    id: "some-id",
    defaultMessage: "This is a message",
  })
  ```

  ✅ instead do this:

  ```typescript
  const message = intl.formatMessage({
    defaultMessage: "This is a message",
  })
  ```

### Integration with Lokalise

> For more information read about [the workflow below](#markdown-header-the-workflow).

#### Message extraction from codebase

Extracts the messages from calls to `intl.formatMessage()` and other supported methods on `intl`.

Running the following command will generate a JSON file at `./i18n/tooling/extracted.json`. The format of this file is for consumption by Lokalise. This JSON file is what gets uploaded to Lokalise.

```bash
yarn workspace @scandic-hotels/scandic-web i18n:extract
```

#### Checking for changes between codebase and Lokalise

> _NOTE_: Diff only considers the English language.

It is recommended to download the latest labels from Lokalise to make sure you have the latest before diffing. See below.

- Run the message extraction above.
- Run `yarn workspace @scandic-hotels/scandic-web i18n:diff`

#### Message upload to Lokalise

Set the environment variable `LOKALISE_API_KEY` to the API key for Lokalise.

Running the following command will upload the JSON file, that was generated by extraction, to Lokalise.

It supports the different upload phases from Lokalise meaning that once this command completes the messages are available for translation in Lokalise.

```bash
yarn workspace @scandic-hotels/scandic-web i18n:upload
```

#### Message download from Lokalise

Set the environment variable `LOKALISE_API_KEY` to the API key for Lokalise.

Running the following command will download the translated assets from Lokalise to your local working copy.

_DOCUMENTATION PENDING FOR FULL WORKFLOW._

```bash
yarn workspace @scandic-hotels/scandic-web i18n:download
```

#### Message compilation

Compiles the assets that were downloaded from Lokalise into the dictionaries used by the codebase.

_DOCUMENTATION PENDING FOR FULL WORKFLOW._

```bash
yarn workspace @scandic-hotels/scandic-web i18n:compile
```

#### Convenience script targets

Extract and upload: `yarn workspace @scandic-hotels/scandic-web i18n:push`
Download and compile: `yarn workspace @scandic-hotels/scandic-web i18n:pull`
Extract, upload, download and compile (push && pull): `yarn workspace @scandic-hotels/scandic-web i18n:sync`

### The workflow

We use the following technical stack to handle translations of UI labels.

- [react-intl](https://formatjs.io/docs/getting-started/installation/): Library for handling translations in the codebase.
- [Lokalise](https://lokalise.com/): TMS (Translations Management System) for handling the translations from the editor side.

A translation is usually called a "message" in the context of i18n with react-intl.

In the codebase we use the [Imperative API](https://formatjs.github.io/docs/react-intl/api/) of react-intl. This allows us to use the same patterns and rules regardless of where we are formatting messages (JSX, data, utilities, etc). We do not use the [React components](https://formatjs.github.io/docs/react-intl/components/) of react-intl for the same reason, they would only work in JSX and would possibly differ in implementation and patterns with other parts of the code.

To define messages we primarily invoke `intl.formatMessage` (but `intl` has other methods for other purposes too!). We take care not to name the message, we do that by **not** passing the `id` attribute to `formatMessage`. The reason for this is that we also have implemented the [@formatjs/cli](https://formatjs.io/docs/tooling/cli) and the SWC plugin. Due to the SWC plugin being a fairly new project and also due to version mismatching reasons, we are using a pinned version of the SWC plugin. Once we upgrade to Next.js 15 we can upgrade the SWC plugin too and skip pinning it. Together, these two are responsible for allowing us to extract defined messages in our codebase. This optimizes the developer workflow by freeing up developers from having to name things and to not be wary of duplicates/collisions as they will be handled by the extraction tool and Lokalise.

Example of a simple message:

```typescript
const myMessage = intl.formatMessage({
  defaultMessage: "Hello from the docs!",
})
```

In cases where extra information is helpful to the translators, e.g. short sentences which are hard to translate without context or we are dealing with homographs (words that are spelled the same but have different meanings), we can also specify a `description` key in the `formatMessage` call. This allows the tooling to extract all the different permutations of the declared message along with their respective descriptions. The same sentence/word will show up multiple times in Lokalise with different contexts, allowing them to be translated indivudually. The description is intended to assist translators using Lokalise by providing context or additional information. The value is an object with the following structure:

```typescript
description = string | {
  context?: string // natural language string providing context for translators in Lokalise (optional)
  limit?: number // character limit for the key enforced by Lokalise (optional)
  tags?: string // comma separated string (optional)
}
```

Examples of a homograph with different context:

```typescript
const myMessage1 = intl.formatMessage({
  defaultMessage: "Book",
  description: "The action to reserve a room",
})
const myMessage2 = intl.formatMessage({
  defaultMessage: "Book",
  description: "A physical book that you can read",
})
```

Examples with a (contrived) sentence:

```typescript
const myMessage1 = intl.formatMessage({
  defaultMessage: "He gave her a ring!",
  description: "A man used a phone to call a woman",
})
const myMessage2 = intl.formatMessage({
  defaultMessage: "He gave her a ring!",
  description: "A man gave a woman a piece of jewelry",
})
```

#### Diagram

A diagram showing the high level workflow of translations. It is currently a manual process syncing messages to and from Lokalise into the codebase.

[![](https://mermaid.ink/img/pako:eNqdVM1u2zAMfhVC5_YFcthhaw8bug5Ye2rcA2PRthBZMiRqWVD03UfFipwtbVBMF1HkJ_Ljj_SiWq9JrVRn_a4dMDDc_Wxc40BWTJs-4DRAGwiZYP1l3jP2eYbkdUO_yPqJQpzt60YtqkY9w_U1aOqMowgjxYi9CMYBDwQ5-gYjCeYTfDa8Se2WuPqpGnEzBySnz-jRbw7YMqxvi_AuwQJ4i-GILqG1ewjJQWyDmRgYQ0-yDcjHIBdSQKchTdajjhAoJsvG9fDt4cc9sIc7v0VrSqbHw8LnqLmYqIBdtIdWPFbxn2RvtWEfYrWL76Iqie582EbYGV78Ge_iX7xOb3-ImXFMImVmX6v4bhsq5H8aof3OzUWuneiCH5cCCxd_YbhOg5_PV17n0MyLg-l7oQmbZKw-dFuTtHtfipkmLUh9XtR7Ymu6_WnconqrpOWt5Ytl5AqkzHY21DmYTctYZGNtxWxUV2qkMKLR8spfsq5RUpxR-rkSUWPYNqpxr4LDxP5h71q14pDoSgWf-kGtOrRRTnN-NwbF-Vi1E7on75czHWbt-_ypHP6W1z--V4Yq?type=png)](https://mermaid.live/edit#pako:eNqdVM1u2zAMfhVC5_YFcthhaw8bug5Ye2rcA2PRthBZMiRqWVD03UfFipwtbVBMF1HkJ_Ljj_SiWq9JrVRn_a4dMDDc_Wxc40BWTJs-4DRAGwiZYP1l3jP2eYbkdUO_yPqJQpzt60YtqkY9w_U1aOqMowgjxYi9CMYBDwQ5-gYjCeYTfDa8Se2WuPqpGnEzBySnz-jRbw7YMqxvi_AuwQJ4i-GILqG1ewjJQWyDmRgYQ0-yDcjHIBdSQKchTdajjhAoJsvG9fDt4cc9sIc7v0VrSqbHw8LnqLmYqIBdtIdWPFbxn2RvtWEfYrWL76Iqie582EbYGV78Ge_iX7xOb3-ImXFMImVmX6v4bhsq5H8aof3OzUWuneiCH5cCCxd_YbhOg5_PV17n0MyLg-l7oQmbZKw-dFuTtHtfipkmLUh9XtR7Ymu6_WnconqrpOWt5Ytl5AqkzHY21DmYTctYZGNtxWxUV2qkMKLR8spfsq5RUpxR-rkSUWPYNqpxr4LDxP5h71q14pDoSgWf-kGtOrRRTnN-NwbF-Vi1E7on75czHWbt-_ypHP6W1z--V4Yq)

The following is a diagram showing how all the parts interact with each other. Note that interacting with Lokalise in any way does **NOT** trigger a build and deploy. A manual action by a developer is required to deploy the latest translations from Lokalise. (Once the manual process reaches maturity we might try and automate it)

[![](https://mermaid.ink/img/pako:eNqdUsFqwzAM_RXh8_IDYewwusvoOlhvIxc1VhITxwq2vCyU_vuchKVlLRvMF0uypaf3eEdVsiaVq8ryUDboBbZvhYN0nrQR9gGyDAb2bYDBSAPi0QWLYtgFuM-yB9hyi9YEWro29EGWe1oaNVXGUYCOQsA6BcaBNAQT6AEDwTTg0cghli3JrQkduojWjuCjg1B60wsI-prS1aAAfaaNSvkFAp2G2FtGHeB5_7oD4XVnuCZw8fQnuObBLYNX9Mpzd55hXAK7Inxm-B_GJXe9sZeifq9B-gf8DXXXdIISb-p6gj1EY_WslKYk1Th37kisqcalT92pjnyHRiezHKdaoRKxjgqVp1CjbwtVuFP6h1F4P7pS5eIj3SnPsW5UXqENKYu9RqGNwdpjt1Z7dO_M55xm870s3pwtevoCSUvs9A?type=png)](https://mermaid.live/edit#pako:eNqdUsFqwzAM_RXh8_IDYewwusvoOlhvIxc1VhITxwq2vCyU_vuchKVlLRvMF0uypaf3eEdVsiaVq8ryUDboBbZvhYN0nrQR9gGyDAb2bYDBSAPi0QWLYtgFuM-yB9hyi9YEWro29EGWe1oaNVXGUYCOQsA6BcaBNAQT6AEDwTTg0cghli3JrQkduojWjuCjg1B60wsI-prS1aAAfaaNSvkFAp2G2FtGHeB5_7oD4XVnuCZw8fQnuObBLYNX9Mpzd55hXAK7Inxm-B_GJXe9sZeifq9B-gf8DXXXdIISb-p6gj1EY_WslKYk1Th37kisqcalT92pjnyHRiezHKdaoRKxjgqVp1CjbwtVuFP6h1F4P7pS5eIj3SnPsW5UXqENKYu9RqGNwdpjt1Z7dO_M55xm870s3pwtevoCSUvs9A)
