You can choose different intention options for Scala multi-line strings. Place your cursor on the string and press
For example, if you select Convert to "String" option, you will see the following result:
The multi-line string is converted to the one-line string.
You also have an ability to insert different intentions. For examle, insert you can choose option Insert gap with concatenation. For the Scala version 2.10 and later you also have the ability to convert the inserted string into interpolated stringone.
Now you can convert to interpolated strings.