.properties

Trailing space is significant and presumed to be trimmed as required by the consumer.

Comment lines in .properties files are denoted by the number sign (#) or the exclamation mark (!)

[3] In Java 9 and newer, the default encoding specifically for property resource bundles is UTF-8, and if an invalid UTF-8 byte sequence is encountered it falls back to ISO-8859-1.

[4][5] Editing .properties files is done using any text editor such as those typically installed on various Operating Systems including Notepad on Windows or Emacs, Vim, etc.

[8] SAP uses .properties files for localization within their framework SAPUI5 and its open-source variant OpenUI5[9] There are many Node.js (JavaScript/TypeScript) options available on Npm's package manager.