[v4] New translations root

[afbora]

This PR …

This is K4 version of #6212. Doesn't include a breaking change.

Fixes

• External language variables setup no longer works since K4's language views External language variables setup no longer works since K4's language views #6176

Features

• New translations root

$kirby = new Kirby([
    'roots' => [
        'translations' => __DIR__ . '/site/translations',
    ],
]);

Breaking changes

None

Ready?

• Unit tests for fixed bug/feature
• In-code documentation (wherever needed)
• Tests and checks all pass

For review team

• Add changes to release notes draft in Notion
• Add to website docs release checklist (if needed)

[bastianallgeier]

Wouldn't it make sense to even unset it here?

[afbora]

Seems setting empty array is correct.

With set empty array:

<?php

return [
    'code' => 'en',
    'default' => true,
    'direction' => 'ltr',
    'locale' => [
        'LC_ALL' => 'en_US'
    ],
    'name' => 'EN',
    'translations' => [

    ],
    'url' => NULL
];

With unseting:

<?php

return [
    'code' => 'en',
    'default' => true,
    'direction' => 'ltr',
    'locale' => [
        'LC_ALL' => 'en_US'
    ],
    'name' => 'EN',
    'url' => NULL
];

[afbora]

I didn't understand the unit test coverage.

For ex: I added LanguageTranslations::get tests with @covers notation but shows still uncovered.

Changes:
https://github.com/getkirby/kirby/pull/6216/files#diff-4e3a14d5dc988b6b8165c6ab49bbe0a32cf21c4c141054da017fe0730e83bf5aR54-R82

Codecov:
https://app.codecov.io/gh/getkirby/kirby/pull/6216/blob/src/Cms/LanguageTranslations.php#L34