If you're writing (or using) a module that stores information in Drupal's variable table there might be the need to change the values of your variables depending on the language your site is currently viewed in.
To do so you'll need i18n and its submodule Variable Translation enabled. To make a variable multilingual you typically head over to
admin/config/regional/i18n/variable, check the desired variable and save your settings. But, what if your module's variable doesn't show up here? That means your module didn't implement
hook_variable_info, provided by the Variable Module. Luckily it really is a piece of cake
implementing it. Just create a file called yourmodule.variable.inc inside the module's root directory. You could also put it in the main module file, but having a separate file is the cleaner approach. The correctly named include file will be loaded automatically.