In that scenario, you need a bit of text-mode trickery. Workfront understands the selections in a multi-select dropdown as a comma-separated string rather than independent items. So you can use the 'REPLACE' formula to replace all commas in the string with the code for line-break as below.
Caution: The moment you hit save, Workfront will automatically remove one of the two slashes in the formula below. When you need to edit again, you have to put that second escape slash back each time.
The only thing I've never figured out is how to make it show the field label, in the case where you have different items in the value vs label for each item in the dropdown. This will only get you the value of the field, which isn't always meant to be human-readable.
displayname=LA Languages
linkedname=direct
textmode=true
valueexpression=REPLACE({DE:LA Languages},",","\\u000A")
valueformat=HTML
