For the majority of people their regularly used language is limited to one, however, HTML - the web description system - is not bound to that specific language. Do not forget, HTML is an international standard and the Web is for the world. So are web browsers. Today's browsers are designed to handle multi-lingual environment. I mostly use US English language but occasionally visit pages written in Japanese language. If you never use more than one language please dismiss this page which probably is none of your interest.
My choice of browser is a Netscape Navigator(Communicator). Although there are different Netscape browsers prepared for each language system (English, French, German, Japanese, ...), all can handle multiple language presentation as long as it runs under an operating system supporting those languages. Roughly speaking, the difference among them is only in which language menu and dialog boxes are presented. Based on the choice of language (character encoding scheme) you select from the View:Encoding menu, the browser chooses appropriate font set and uses language specific presentation rules.
Since English character set is a subset of Japanese character set, at least in computer systems, all English alphabets are correctly displayed while keep selecting Japanese encoding. However, the display font for Japanese is often limited to smaller number of font set than the English alphabet fonts, the exact visual representation of English pages on the screen slightly differs between selection of Western(ISO-8859-1) encoding and Japanese (Auto-Detect).
Some of my friends also use two language systems, English and Japanese and most of them are too lazy choosing appropriate language systems for each page so they simply keep Japanese encoding even when they visit English pages. I personally can not stand this custom because many pages look quite ugly if you select wrong language system, although you can perfectly read them. It is simply a matter of appreciation of the appearance. Yet, I do care about that small difference. (And this appreciation of the taste is the main reason I keep using Macintosh.) The price I have to pay for that is I manually have to select appropriate language system when I visit different language pages.
Selecting the appropriate language encoding scheme every time switching to a different language page is a tedious task. The browser is a computer software and the a web page is computer data that browser processes. Why can't data describe itself in which language it is written? Why can't pages instruct browsers which language system to use? The answer is "Yes they can". HTML has a mechanism to tell the browser in which character set a page is written. For example this page has a following tag in its header.
<meta HTTP-EQUIV="Content-Type" CONTENT="text/html;CHARSET=ISO-8859-1">
So that the browser correctly selects Western(ISO-8859-1) character set to display this page.
Now click this one (a). The page's header has a tag:
<meta HTTP-EQUIV="Content-Type" CONTENT="text/html;CHARSET=ISO-2022-JP">
This tag instructs the browser to automatically select the Japanese character set so that no matter your browser setting is, the content is displayed correctly in Japanese character set. If the same page lacks this single line of important tag the page may be displayed as full of garbage characters like this one (b) depending on your browser's setting. If you do not see the garbage characters try this one (c) which forces the browser to use western character set. All three pages are identical except the header information describing the character set information. Try switching among (a), (b) and (c) while changing the browser's default character set. Also switch to each page and change the browser's character setting while viewing each page. (a) is always displayed correctly regardless of browser setting. (b) depends on browser setting. (c) displays garbage always. You can view the page sources and compare them each other.
Next let's take a look at the difference between viewing an western character page with Western character set and Japanese character set. See how good and bad they appear. Contents are the same except the bad one forces the browser to use Japanese character set.