... I know in Greek, you can usually drop the personal pronoun; is this is the case in Spanish?
Well, for most verbs you can, but for gustar (to like) you can't because there would be no way to know who likes what. The conjugation of the verb gustar in Spanish is different in that its form is chosen based on what is liked, not who is liking it.
The problem of making an automatic translator breaks down to something like this:
First you need to be able to directly translate the words.
IF you manage that to any reasonable degree (around 5,000 to 10,000 words), you can then move on to conjugation of verbs and arrangement of subjects and such so that things make more sense.
IF you manage to make it translate the regular stuff, you might want to try your hand at dealing with irregular things that break the rules you just spent most of your time trying to get to work in the first place.
IF, and only IF you manage that, the last thing you might try is translating common phrases and such that break every rule thus far. For instance, directly translating "What's up?" to other languages will cause problems because whoever receives the message might start looking at the sky wondering what you saw.
IF, by some unholy, wicked and twisted bit of programming you manage that, then you somehow found the secret to eternal life. PROOF: Languages change all the time. You'd have to always be updating your code to make sure it works.