Most of our clients have bilingual (French and English) websites. The Language Switcher Block is a great way to switch between languages, but we often don't want to display the active language. For example, on a French-language page, we want to have a link to English (not French and English).
Our solution is to add the following css either to your theme, or, if you are using a contrib or core theme, to css injector. (Messing with a core or contrib theme will cause your changes to be lost during upgrades):