Installation

Place this repository in /app/code/HyvaCamp/I18n.

Patch the following files until we find out how to do this properly:

diff --git a/setup/src/Magento/Setup/Module/I18n/ServiceLocator.php b/setup/src/Magento/Setup/Module/I18n/ServiceLocator.php
index a3964d7d..9c4773c0 100644
--- a/setup/src/Magento/Setup/Module/I18n/ServiceLocator.php
+++ b/setup/src/Magento/Setup/Module/I18n/ServiceLocator.php
@@ -50,13 +50,13 @@ class ServiceLocator
     {
         if (null === self::$_dictionaryGenerator) {
             $filesCollector = new FilesCollector();
-
             $phraseCollector = new Parser\Adapter\Php\Tokenizer\PhraseCollector(new Parser\Adapter\Php\Tokenizer());
             $adapters = [
                 'php' => new Parser\Adapter\Php($phraseCollector),
                 'html' => new Parser\Adapter\Html(),
                 'js' => new Parser\Adapter\Js(),
                 'xml' => new Parser\Adapter\Xml(),
+                'json' => new \HyvaCamp\I18n\Parser\Adapter\Json(),
             ];
 
             $parser = new Parser\Parser($filesCollector, self::_getFactory());

diff --git a/setup/src/Magento/Setup/Module/I18n/Dictionary/Options/Resolver.php b/setup/src/Magento/Setup/Module/I18n/Dictionary/Options/Resolver.php
index 2f58b5fe..11817298 100644
--- a/setup/src/Magento/Setup/Module/I18n/Dictionary/Options/Resolver.php
+++ b/setup/src/Magento/Setup/Module/I18n/Dictionary/Options/Resolver.php
@@ -90,6 +90,11 @@ class Resolver implements ResolverInterface
                         'paths' => array_merge($moduleDirs, $themeDirs),
                         'fileMask' => '/\.xml$/'
                     ],
+                    [
+                        'type' => 'json',
+                        'paths' => array_merge($moduleDirs, $themeDirs),
+                        'fileMask' => '/\.json$/'
+                    ],
                 ];
             } else {
                 $this->options = [
@@ -97,6 +102,7 @@ class Resolver implements ResolverInterface
                     ['type' => 'html', 'paths' => [$this->directory], 'fileMask' => '/\.html/'],
                     ['type' => 'js', 'paths' => [$this->directory], 'fileMask' => '/\.(js|phtml)$/'],
                     ['type' => 'xml', 'paths' => [$this->directory], 'fileMask' => '/\.xml$/'],
+                    ['type' => 'json', 'paths' => [$this->directory], 'fileMask' => '/\.json$/'],
                 ];
             }
             foreach ($this->options as $option) {

Running

Collect phrases (e.g. just inside hyva cms module):

php bin/magento i18n:collect-phrases vendor/hyva-themes/commerce-module-cms/src/components-base/etc/hyva_cms/