(Affects 6.0.1, EditionEnterprise, (bundle) 6.0.1 (Snapshot: 2019.02.19 17:27:28))

To reproduce:

• Create a content app from a content type definition
• Turn the i18n on for a text field in it.
• Go to the app's dialog and switch to a different language. The label for that field - as well as any other label - will probably disappear, at least with the second switch of the language. 

See for example in the following videograb:

vokoscreen-2019-02-20_17-36-01.mkv

The grab was created after completing the https://documentation.magnolia-cms.com/display/DOCS61/Content+Types+tutorial.

In its almost last step
https://documentation.magnolia-cms.com/display/DOCS61/Part+II+-+Complex+content+types+and+security+set+up#PartII-Complexcontenttypesandsecuritysetup-Settingthei18npropertyinmodelproperties
it's the description property where the i18n is set to true.

Tested also on 6.0 released but the issue doesn't seem to appear there.