There is no symbol for line continuation in Kotlin. As its grammar allows spaces between almost all symbols, you can just break the statement:
val text = "This " + "is " + "a " +
"long " + "long " + "line"
However, if the first line of the statement is a valid statement, it won’t work:
val text = "This " + "is " + "a "
+ "long " + "long " + "line" // syntax error
To avoid such issues when breaking long statements across multiple lines you can use parentheses:
val text = ("This " + "is " + "a "
+ "long " + "long " + "line") // no syntax error
For more information, see Kotlin Grammar.