Dart
Google will make your dart language be interpreted natively by the browser.
Actually, it already does! There is a version of Chromium that already runs directly scripts written in Dart - the Dartium.
The trend is that the Dart language will occupy quite a lot of space within a few years.
If other browsers support Dart then its use may be as prominent as Javascript today!
Dart is currently "compiled" for Javascript, meaning you write the program in Dart and the IDE translates to Javascript, making it a usable solution from now on.
CSS, HTML, XML, XSLT...
HTML, XML... the "L" is "Language", ie, language. Are languages of mark-up, non-languages of programming. But, anyway, these are languages that we use in browser, javascript-free.
Similarly, CSS and XSLT are languages of style-sheet that browsers also handle.
And these are not all the "languages" that both we developers and the browsers can handle in the assembly of pages and web applications on the client side. However, as I said, they are not languages programming.
Other Languages
A browser is a type of software that depends on an entire ecosystem. No use a genius to devise a browser revolutionarily great, or even bring the real browser which will be effectively used 50 years from now... to the present day. Such browser would be useless, because there is no website or web page prepared for it.
It’s like traveling through time and taking a television set to 100 or 200 years ago, or more: in which outlet turn on the bug? What programs will it capture, whether by antenna, satellite or cable? There is no electricity network, no stations: the television set, even if it is 3D, LED of last generation, is a useless traste.
In the evolutionary point of IT that we are today, the browser, as it is, it has A (programming) LANGUAGE, and that language is the Javascript. And that’s the end of it. We can analyze and discuss the historical, social, political, economic and technological events of how the evolution took place up to this point... but the fact is this: Javascript is the language of the internet, the web, the client-side, the browser, the browser. Mobile devices can have their native resources... but everyone will have the Javascript in their browsers.
To this animal that is the browser, today, accept, understand and run C, Ruby, PHP, Python, Perl, COBOL, Pascal, Basic, LOGO, Ada, Haskell and Fortran... well... honestly... it’s this idea to me that doesn’t make much sense. There might even be some standard web to make this connection... but provide support for a multitude of languages built-in in the browser is a nonsense. Such browser would be the software heaviest of all time!
Even if a standard to "connect" other languages installed in the host operating system to the browser... then only those who have the language installed could enjoy it. Nothing so different than what we already have today, with Flash (Actionscript), Java, etc.. You mean, through a plugin or a new standard, the user will need to install support for that other language(s) (s).
Otherwise, embed the support into the browser, as I have already said, it seems to me evidently impracticable and absurd, for the simple technical fact of extrapolating the already extrapolated scope of a... browser. That’s how I understand it.
Thanks, that’s the kind of answer I was looking for. In fact, alternative languages either "compile" for Javascript or are interpreted in Javascript, both strategies with their disadvantages (e.g., poor performance). Now I am better understanding the technical challenges that make it impossible to open up more languages.
– mgibsonbr