The article explains why, in some instances, there is an issue with retrieving the value of a user custom property when using multiple languages.

This occurs because the user custom property is not language-agnostic at this time. The property changes language based on the last editor's site language preference.

When a subsequent call is made via the API or in the workarea, the value is empty if the current language does not match the last editor's language settings for that property.

The recommendation is to keep the property to one language for maintenance reasons. This practice prevents retrieval issues if the API is specified to that regulated language. 

If the property must be language specific, like a translated text, the recommendation is to have separate properties.