Properties files
Properties files are text files with the .properties extension, containing localization strings in the form of key and value pairs that can be accessed and rendered in the UI. IntelliJ IDEA marks these files with the following icon: 
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IntelliJ IDEA also recognizes properties files in XML format. They are marked with the icon 
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Several properties files with the same base name and a language-specific suffix can be combined into a resource bundle for convenience.
Create a properties file
Right-click a directory where you would like to create the file.
From the context menu of the target directory, choose .
In the New File dialog, type the filename with the corresponding extension .properties, and click OK.
Encoding of properties files
The standard Java API is designed to use the ISO 8859-1 encoding for properties files. You can use escape sequences for characters that are not defined by this encoding. Alternatively, you can define the default encoding for properties files on the project level and use a different API that can read properties files in the encoding you have defined.
Configure default encoding for properties files
In the Settings/Preferences dialog Ctrl+Alt+S, select .
Select the encoding from the Default encoding for properties files list.
If necessary, enable Transparent native-to-ascii conversion to show national characters (those not defined in ISO 8859-1) in place of the corresponding escape sequences.
For more information, see Encoding.