simple algorithm to encrypt/decrypt a text file I need to write a first program in one language that saves data in a text file, and write a second program in a second language to decrypt that file. The two languages in question don't include any crypto libraries, so I'm on my own.

Could someone recommend, point me to, or summarize a simple algorithm (pseudo code) that provides some level of basic encryption?

I don't have much experience in this area, but if you can summarize clearly in pseudo-code, I can implement it (don't assume prior knowledge).

It doesn't have to be bullet-proof, but just something that deters the user from understanding the text file. Something more secure than just a simple character-substitution (1 for 1), like perhaps a key that generates a random string used to XOR or similar complexity. I have no idea where to start.
My advice would be to use a stream cipher.

First of all, it is easy to implement, because you won't have to think about dividing into blocks, padding, etc..

Secondly, the idea of stream ciphers is very easy: you generate a  pseudorandom sequence of bits out of the private key. Then you XOR this sequence with a plaintext. You will only have to code the generation, the rest is elementary. 

Finally, there are very easy stream ciphers, e.g.  RC4 http://en.wikipedia.org/wiki/RC4;  another example is Salsa20 http://en.wikipedia.org/wiki/Salsa20

And when I say "simple" I mean not only the amount of lines of code, but also the ease of debugging/ flaws search.