Finalize the Great Translation Purge

• waits for !1663 (merged)
• closes #238 (closed)
• closes &7 (closed)

What does this MR do?

• finish translation-refactoring: Settings* and the very basics of Report*/Quiz*
• replace hardcoded role logic with new getRoleName helper
• remove all PHP translations! and associated infrastructure
  • this includes moving all implicit form-field translations to YAML
• update i18n devdocs

How confident are you it won't break things if deployed?

Much to my surprise, the build for this is green. It would be pretty good to test the changes through and through, since it's related to core functionality (displaying text)

How to test

Basically: do things and check if the text you are seeing is what you expected. A lot.

Checklist

• no added functionality that wasn't already covered by tests
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• use "state:" labels to track this MR's state until it was beta tested
• added an entry to CHANGELOG.md
• add a short text that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in Beta Testing Repo:
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...). how this change can be tested.
  • Be aware, that also non technical people should understand.

docs/internationalization.md

 # Internationalization
 
 We want the code to be free from German-specific texts to enable non-German speakers to use the site and to make it easier for groups in other countries to use the code.
-Unfortunately, we are not there yet. At the moment there are three ways how fixed text on the website is given in the source code:
+Unfortunately, we are not quite there yet, but a lot of progress has been made and the remaining hardcoded strings are indicative of obvious legacy code.
 
-- Hardcoded text (obviously legacy code), e.g.
+We use the Symfony `TranslatorInterface` to replace translation keys (given in code) with their translated values. Translations are read from files in YAML format: for German that would be `/translations/messages.de.yml`.
+Aside from those German strings, there are four mail ways in which fixed text on the website can be given in the source code with our translation mechanisms:
+
+- In PHP frontend/view code
+Classes derived from Control and View already contain the TranslatorInterface, which is accessible as `$this->translator`, and its `trans()` function that resolves translation keys.  
+Other helpers are including it like this:
+```
+use Symfony\Contracts\Translation\TranslatorInterface;
+// instantiate or inject (usually autowired)
+$this->translator->trans('fsp.acceptName', ['{name}' => $foodSharePoint['name']])
+```
+- From JavaScript code
+In `client/src/i18n.js` we build a basic replacement function that imports translation resources, replaces variables if needed, and returns the translated value if one exists. Fallbacks are implemented for English and German, which are currently the only languages for which we bundle translations.  
+To use this function elsewhere, import the module like so:
 ```
-$this->pageHelper->addContent('<...>Updates-Übersicht<...>')
+import i18n from '@/i18n'
+pulseInfo(i18n('basket.not_active'))
 ```
-Do not create more of this hardcoded German!
-- References to the translation files in `/lang/DE/....php` via the function `s` in `/src/Utility/TranslationHelper.php`, e.g.
+- As part of Vue templates
+In `client/src/vue.js` we define the `$i18n` prototype and attach it to all Vue templates. This is the preferred way of frontend translation. If you're translating component parameters, make sure to :bind them accordingly: `:title="$i18n('button.clear_filter')"`
+- As part of Twig templates (Legacy)
+The [`trans` filter](https://symfony.com/doc/current/translation/templates.html#using-twig-filters) allows passing translation keys to the translation engine from Twig files. Examples:
 ```
-$this->translationHelper->s('close_foodbaskets')
+{% embed 'components/field.twig' with {'title': 'events.bread'|trans} %}
+<h4>{{ 'dashboard.push.title'|trans }}</h4>
 ```
-- References to the translation file `/lang/lang.de.yml`.
-TODO: describe how to use this data. It has something to do with symfony.
-This is the way to go when you create new text on the website.
+Do not create more of these unless you really know what you're doing! You will need to be very careful with the syntax for replacing variables (`|trans({'%name%': name})`).