In order to implement Tet4 I learnt two new languages - JavaScript (or JScript, or ECMAScript - the language has a bit of an identity crisis) and PHP. Why PHP? It's installed on my web hosting server and seems to have a huge community of people writing code in it and pre-written scripts. It may not be the ideal language for writing web server apps, but it does seem to be the most well-supported.
JavaScript seems to be a very clean, pretty language. The whole closure thing seemed a bit weird at first but once I understood that "class" is spelled "function" and "public" is spelled "this." I got to rather liking it. I especially like how each scope has access
to the variables from all the outer scopes - that saves a lot of messing about. It's very well integrated with the browser - manipulating the DOM feels very natural and not tacked on.
PHP on the other hand is a bit of a mess. It is as if its designers had a little spinner with markings "C, C++, Perl" which they spun each day to decide what languages features to copy that day. If JavaScript was sent by God, surely PHP was sent by the devil.
W3Schools has been an excellent reference for learning all this.
I have to say though that automatically promoting integers to double-precision floating point numbers on overflow is weird. On IE7, computing the value of 1111111111*1111111111 gives 1234567900987654400 (you can easily see this is wrong because it's even). This caused a rather hard-to-debug problem with my random number generator (which assumed that when multiplying two 32-bit integers together, at least the low 32 bits of the result should be correct). If you're going to automatically promote numbers, at least have the decency to use a multiple-precision integer library - there are lots around.