Classic Commerce can be used in any one of the 12 supported languages. The first step is to switch your CMS to the language that you want to use. You do this in the Settings > General page by selecting from the dropdown box.
Classic Commerce has a directory containing all of the templates that are used by your site. These files hold the markup and template structures for the front end pages and emails generated by your store. It is possible to override template files and instead use customised versions that will be more suitable for your particular application.
Code snippets are a great way to add minor functionality or make small modifications to your Classic Commerce site without the need for extra plugins. The best way to use code snippets is to put them in a separate plugin that is added to your site, specifically for this purpose.