RESW/RESX files are localization files used by C#/.NET software. These two types of files have different resx and resw extensions, but the content and storage format are the same. The only difference is the use of these types of files in the program development process.

A RESW/RESX file is an XML file that contains the strings that you want to translate into different languages or paths to images. The resource file contains key/value pairs. Each pair is an individual resource. Key names are not case sensitive. For example, a resource file might contain a resource with the key Button1 and the value Submit.

A resx/resw files contains a standard set of header information, which describes the format of the resource entries and specifies the versioning information for the XML used to parse the data.

Following the header information, each entry is described as a name/value pair, very similar to the way in which strings are specified in a .txt file. A name/value pair in the resx/resw format is wrapped in XML code, which describes string or object values. When a string is added to a .resx file, the name of the string is embedded in a <data> tag, and the value is enclosed in a <value> tag,

Documentation

ASP.NET Web Page Resources Overview
Resources in .Resx File Format