Add support for a new translation in Whitehall

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Last updated: 13 May 2021

Before starting, it’s worth checking the language tag that is being added is correct: it should be compatible with the IETF Language Tag syntax and use correct ISO 639 codes (with optional ISO 15924 or ISO 3166 subtags where appropriate). This is important to ensure maximum compatibility with accessibility feature such as screen readers. Some other useful reading includes Rails Translation Manager and Whitehall Internationalisation guide.

1. Update Government Frontend

Example PR

In Government Frontend:

Add the new locale to config/application.rb and config/locales/en.yml in alphabetical order

Run the following commands to generate the locale files from the English template:

$ export LOCALE=<new_locale>
$ rake "translation:export[tmp/locale_csv,en,${LOCALE}]"
$ rake "translation:import[${LOCALE},tmp/locale_csv/${LOCALE}.csv]"

In config/locales/<new_locale>.yml add the language translation under the language_names key.

For example:
```
 it:
   language_names:
     it: italiano
```

2. Update Whitehall

Example PR

In Whitehall:

Add the new locale to lib/whitehall.rb and config/locales/en.yml in alphabetical order

Run the following commands to generate the locale files from the English template:

$ export LOCALE=<new_locale>
$ rake "translation:export[tmp/locale_csv,en,${LOCALE}]"
$ rake "translation:import[${LOCALE},tmp/locale_csv/${LOCALE}.csv]"

In config/locales/<new_locale>.yml add:
- the language direction under the i18n.direction key
- the appropriate boolean under the i18n.latin_script? key
- the language translation under the language_names key
For example:
```
 it:
   i18n:
     direction: ltr
     latin_script?: true
   language_names:
     it: Italiano
```