What is your requirement , do u have to merge two value list or page list ?  For merging two arrays below is the code 

String a[]={"A","E","I"};
String b[]={"O","U"};
List list =newArrayList(Arrays.asList(a));
list.addAll(Arrays.asList(b));
Object[] c = list.toArray();

Follow this thread as well,

https://pdn.pega.com/community/product-support/question/concat-array

Hope either of the posts helps.

The best way would be in a script. If you wanted to do so in an automation, it could look like the screenshot attached (assuming both were single width string arrays). I am using the Join and split methods to put together and break apart the arrays using the value stored in the delimiter variable. In my example, I made it a comma, but if your list contained commas, then it would need to be something else (maybe a semicolon : or a tilde ~).