Steps to reproduce

1. enable i18n feature for your content app, for example categories app
   1. add i18n flag to the displayName field: https://demoauthor.magnolia-cms.com/.magnolia/admincentral#app:configuration;/modules/categorization/apps/categories/subApps/detail/editor/form/tabs/category/fields/displayName@i18n:treeview:
2. switch your language to French
   1. logout and login afterwards
3. edit a category in the categories app
   

Expected results

1. only in i18n configured languages should be available (English and German)
2. the default language should be selected (English)

Actual results

1. the editor language is preselected
   1. creation and storing of unused content
   2. confusing for the editor

Workaround

Migrate apps to new UI.

Dev notes

Only reproducible in apps using the legacy ui, such as, contacts, assets, etc. In case of contacts-v8 and dam it is not reproducible.

It also happens in legacy pages app, when a dialog is opened.