During the process of creating my first public WordPress theme one thing was very important to me – I wanted the theme to be useful to as many people as possible. To reach this goal, I knew that I would need to make sure that my theme could be used in any language. Luckily, WordPress core provides a few different functions that makes this pretty easy to do. If this is a new topic for you, please read more about Internationalization for WordPress Developers in the codex.
Writing files from code, whether it be from a theme or from a plugin, is generally bad mojo. However understanding why you shouldn’t is confusing to many, and then understanding why you shouldn’t do-it-yourself and should use the WP_Filesystem is even more confusing.
A great writeup by Otto on how, why, and when to use WP_Filesystem to write files from a WordPress theme or plugin, including code samples and a demo plugin.