Thanks for the answers, Alberth. As you can tell, I didn't really looked that much into the logic behind the web translator. But your points are I have a better understanding of the whole process to minimize errors and duplications. I think I will have to rely on the "Related Strings" module to track similar strings and keep everything consistent.
As for the projects on the Dev Zone, I can see the "starred" are the ones I can translate. I'd really love to translate the Japan Set, which is not available on the web translator thing but it's on the projects on the dev zone. Sadly, it seems no one has access to the "subprojects", which seem to be the actual NewGRFs. I'm guessing these can't be translated?
Now, I have a petition: would it be possible to rename the "ownname" of the translation? It currently says "Español mexicano (MX)", which is a little redundant. It should say only "Español (MX)" to suggest the variant from "Español", similar to "Português" and "Português (BR)".
And I'm looking forward to getting the translator validation for ISR, which is still sitting on the issues queue.
edit:
Another thing: I tried to creat a translation for the Android port of the game, but the lang file is missing the gender information (##gender m f). How to proceed in these cases?