I have two xml files in values folder for strings:
From strings.xml I can access string as follows:
String str = getString(R.string.app_name);
How can I directly access from new_strings.xml?
By the same way you're accessing the values in strings.xml file.
Example :
strings.xml :
<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="app_name_1">First app name</string>
</resources>
new_strings.xml :
<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="app_name_2">Second app_name</string>
</resources>
In your java code you can do :
R.string.app_name_1
R.string.app_name_2 
and you can access both values which are in two different xml files.
As the doc said: file location:
res/values/filename.xml
The filename is arbitrary. 
The <string> element's name will be used as the resource ID.
compiled resource datatype: Resource pointer to a String.
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