JavaScript - Switiching Between Languages

Greeting Everyone,

Can anyone breakdown the differences between programming languages in VERY VERY BASIC plain English? (i.e. HTML use for website format, CSS used for the graphics on the webpage)

Here's what I have questions about:

1. Differences between the most commonly used programming languages for software/web development (Javascript, Ruby on Rails, Phyton, etc.).

2. How do you determine which programming languages to use?

3. What factors are considered?

Thank in advance for the people that reply. =)

I want to have a browser language detection for 2 languages for Explorer and Firefox and struggle a little to make it work.

I don't know really much about JavaScript so I guess I did some grave errors. It works for one language though, but for that I don't really detection.

I am not sure if that's wrong, but I try to look for the 'en-' in the language not to deal separately with en-US, en-AU, en-UK etc.

PHP Code:
<script type="text/javascript">

var str=navigator.language;
x = (str.search(/en-/i));

if ( !(x=='-1') )   {
document.write("English Mozilla");
}

var expl=navigator.browserLanguage;
ex = (expl.search(/en-/i));

if (  !(ex=='-1') )   {
document.write("Englisch1 Explorer");
}

var dm=navigator.language;
d1 = (dm.search(/de-/i));

if ( !(d1=='-1') )   {
document.write("German Mozilla");
}

var dex=navigator.browserLanguage;
dexpl = (dex.search(/de-/i));

if (  !(dexpl=='-1') )   {
document.write("German Explorer");
}

</script>