Use english as fallback language

[AlexGacon]

Checklist

• [X] I've searched through the current issues to make sure this feature hasn't been requested already.

Motivation

When I use a language with a partial translation (for example French), G3W uses the Italian text as placeholder when a text is not translated.

Suggested solution

Having a fallback to English would make G3W easier to use and start with for non Italian speaker.

Alternatives considered

No response

[wlorenzetti]

@AlexGacon just set LANGUAGE_CODE = 'en' into the settings.