Changing Browser Date Formats
You can typically specify several alternatives that will be treated in order of preference. The following example shows a setting in Firefox for someone who would prefer Swiss French pages, but if that is not available would settle for any French, German or English page, in that order.
Often browsers will allow you to select the languages you want from a list. You may also be able to specify custom language preferences. If you do so, you need to use values that will be recognized by the server (see below).
Your preferences should always be ordered from most to least specific, top to bottom. This generally means, if you use multiple subtags then include shorter tags lower down the list.