Oracle translation factory does not support variables and
functions in message values. The file Converter.java contains a
variable that is used for adding platform independent line
separator.

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private static String newline = System.getProperty("line.separator");

private static Object[][] contents = {
        { "key1", "This is a text." + newline + " This is another text." + newline }
    };
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We should change the code to avoid variables in the
message text. We can do it this way:

-------------------------------------
private static Object[][] contents = {
        { "key1", "This is a text.\n This is another text.\n" }
    };

// platform independent line separator
static {
    String ls = System.getProperty("line.separator");
    for(int i=0;i<contents.length;i++) {
        if(contents[i][1] instanceof String){
            contents[i][1] = contents[i][1].toString().replaceAll("\n",ls);
        }
    }
}

If the type of the entry is not String, it will not be changed. So, anything like mnemonic key will not be affected.