V8: Allow localizing content types and properties using language files

[kjac]

Prerequisites

• I have added steps to test this contribution in the description below

Description

If you want to localize content type and property names in the backoffice, you currently have to do it using the dictionary. This is convenient if you have the same languages in frontend and backoffice, but if you don't... well, things get messy

From a conceptual point of view, doing backoffice localization using the dictionary isn't terribly pretty, because the dictionary is pretty much a frontend thing.

So! This PR makes it possible to do the same localization of backoffice names using the language files. The naming follows the same convention as the dictionary based localization; you add the "#"-prefix and then specify the localization key as either [area]/[key] or [area]_[key] :

The corresponding localization file (e.g. en-US.user.xml) would look something like this:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<language>
    <area alias="contentTypes">
        <key alias="home">Name for Home</key>
    </area>
    <area alias="properties">
        <key alias="title">Name for Title</key>
    </area>
</language>

And the result:

Testing this PR

1. Create a content type and localize its name and properties as described above.
2. Create matching localizations in two user language files (e.g. en-US.user.xml and da-DK.user.xml).
3. Test both languages by flipping your backoffice user language.

[emmaburstow]

Hey @kjac

Thanks for the work. If we need you we'll let you know,

Em

[nul800sebastiaan]

This is sweet, thank you kindly! 😄