Add Kotlin test file and build command

Author: angelapwen

tests/multi-language-repo/build.sh

@@ -11,3 +11,5 @@ go build main.go
 if [[ "$OSTYPE" == "darwin"* || "$OSTYPE" == "linux-gnu"* ]]; then
     swift build
 fi
+
+kotlinc main.kt

tests/multi-language-repo/main.kt

@@ -0,0 +1,5 @@
+fun main() {
+    if (true) {
+        println("Hello, World!")
+    }
+}