How many client-side scripting language implementations did you see except JavaScript and VBScript? Like: type=\"text/C++Script\"
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The only languages I have ever seen supported by web browsers in elements are:
The HTML 4 specification gives examples of Tcl, but I've never heard of a browser that implemented this.
In any practical sense (for WWW development), JavaScript is the only (not really a) choice.
There are also various languages (e.g. Dart, TypeScript, ES6/7) which have translators to convert programs to (ES5 flavoured) JavaScript which can then run in browsers.