PageChooser showing pages from all locales in translation page

[enzedonline]

When a translation editor clicks on the Change Page button, it shows pages from all locales:

The editor needs to select the locale filter.

This is quite a confusing display for the editor. By default, the locale filter for the locale being translated into should be already applied (i.e. source locale en, target locale de, the page chooser is filtered to de).

Better still, the chooser should follow the standard of the Wagtail editor page and only show pages from that locale without the option to choose from others. There shouldn't ever be need to link to pages from other locales as following that link would cause the selected language to change.

[enzedonline]

I've just noticed that page choosers on snippets are using the wagtail-localize chooser even on source instance, not just on translated instances.