As a Wikibase editor, while editing I can clearly see in the terms section if a missing Label already falls back to a Label in a particular language or to the `mul` language code. This will help me to decide whether a suitable fallback already exists or if I need to input a new one.
**Mockups:**
{F37114607}
| [[ https://www.figma.com/file/UMHGYSxln03lGx2z7GxzP2/Multiple-languages?type=design&node-id=340-8642&mode=design&t=d0477X8hCtNiYCRO-0 | Link to Figma specs ]] |
**Acceptance criteria:**
[] When the Wikibase Entity is opened for editing on desktop, the first Wikibase language fallback label is used as a placeholder - without being truncated - for all empty Labels.
[] If no fallback label is available, the `mul` Label is used as a placeholder.
[] If there is no `mul` label to be used as default, "Enter a label in <language>" (the current placeholder) should be displayed
[] The `en` Label is not used as the default placeholder for any empty labels, unless it is part of the Wikibase language fallback.
[] The acceptance criteria above can be validated on test.wikidata.org
**Notes**:
* As of this task, the editing interface does not need to be reactive. i.e. the placeholder will not change while entering a label. Only after submit and refresh.
* We can ignore ULS-added languages for now: Wikidata adds languages from ULS (for non-logged-in users, for logged-in users with fewer than 4 UI/Babel-specified languages), it is okay to only apply MUL placeholders for these (where available).