Locale: Browser or OS Setting?

What does it mean when a "locale" is set to e.g. Japanese? Does it mean the browser is set to be ready to recognize Japanese characters? Or, is it more related to an OS setting?

Related to i18n (internationalization and localization), how do we detect that a user who is visiting our site has a e.g. Japanese locale using JavaScript? Will the following simple check suffice?

var us开发者_C百科erLocale = navigator.language || navigator.userLanguage;
if (userLocale.toLowerCase() == 'ja-jp') { ... }

Can a Japanese locale browser return something else rather than ja-jp?

Thanks beforehand.

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First we need to define what Locale is. In the context you are using it is a ISO639 Language Identifier optionally followed by ISO3166 Country Identifier. This is used to determine end user's preferences (like language of localized content or date and time formats and number formats).

Now, Locale could be set in multiple places. OS usually has multiple settings, for example keyboard layout, formatting preferences, language preferences, code pages (for non-Unicode programs), etc.
Apart from that, web browsers usually allow you to choose your own preferences (Safari is an exception here). These preferences are send along with each request to the web server, via HTTP Accept-Language header. This is something you should somehow read on the server side (which unfortunately means some server-side code in PHP, C#, Java, whatever) and maybe passed to your client-side script.
I must state here that something like navigator.language is not the way to go for two reasons:

1. This is not cross-browser compatible, that is other web browsers would require different code. That is if they allow reading this information in the first place.

2. This setting usually refers to web browser's language (the language web browser's user interface is translated to) and has nothing to do with actual user's preference.

So to answer your question: no, this check will not suffice.

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That is mostly an OS/browser setting, controlling e.g. language of the OS, date/time format, decimal point/comma, etc. - in other words, settings that vary in different locales of the world. This has no direct correlation with font/character support.

As far as I know, ja-jp is the only standardized Japanese locale/language combination; but as @Siku-siku.com suggested in the comments "(based on real testings using Japanese version of IE/WinXP) also check for ja because that's one of the available options in the IE language setting."