Take my advice: if you're serious about getting into ROM hacking, ditch those game-specific editors. There's nothing you can't do with a hex editor like HxD and WindHex32 EX. I'll give you everything you need to get started, just let me know if you have trouble.
First of all is my DTE routine, which stands for Dual Tile Encoding. Basically it means that instead of spending one byte spelling the letter 'a', you can have 'ab' with just one byte. This compresses the text significantly, meaning you should have no problem fitting all your text in the ROM. It works like this: each byte has 256 possible values. Since the English alphabet plus numbers and punctuation rarely needs more than 70 values, the rest are free to use. Some are reserved by the game (such as knowing where the line ends, for example), but the majority have no use, and can be used by a DTE routine instead.
Of course, you will need to know which pairs of letters are most common in order to make this work, because you need to write a table inside the ROM of all those pairs. Fortunately, our good friend KingMike wrote a simple program that takes your script and tells you the most common pairs:http://www.romhacking.net/utilities/306/
Next you need a simple way of dumping the text and re-inserting it. Again, I've already done it here.
I used a versatile program called Pointer Tables that will work with almost any game, provided you know how the game works:http://www.romhacking.net/utilities/502/
In this case, I made a table file for all the text characters in the game, found the text and the pointer table for it, and dumped the text. To insert your own text, you just replace what's in the dumped text file with your own.
You can use a different table file of course, which you'll need for Spanish due to the accented letters. I imagine there's a few letters used in English which aren't necessary for Spanish, so you could replace them. Once the text is in there, it's just a matter of changing the pointers to reflect the new text, which thankfully is easier in DW than most other games.
You can get started without worrying about the whole DTE thing, but if you can make a complete script, you can use DTE-Opt to compile your table of pairs, then put it in the ROM, then insert the script with a new table file that includes the pairs (my routine allows between 81 and ED, any more and it would affect things the game uses). For now, don't worry about that, but I have included an IPS patch that takes an original DW ROM and inserts my DTE routine so that it's ready to go. I did the hard part of programming it, so at least that's done.
The patch will work on this ROM, though I'm sure you've dumped your own.
GoodNES name: Dragon Warrior (U) (PRG1) [!].nes
Of course, if all this looks like too much to handle, you can just do the translation and I can put it in the game, but I imagine you decided to do this as hacking practice, so that would defeat the purpose.
Regardless, here's a zip with everything you need: my DTE patch, a table file, and a dump of all the text in the game (it's actually not that much compared to some games). I didn't dump the items, because that would be better to edit within a hex program since there's so little text, and space is a concern.
As for programs, I recommend HxD for general hex editing, WindHex32 EX for editing little bits of text (like the item list), and the two programs from this site that I've already mentioned. You'll also need a tile editor like Tile Molester to draw new characters for your Spanish alphabet, but remember you're limited to removing existing letters, because unlike in a Japanese game, you don't have a huge syllabary to replace.
So here's the zip file, let me know if you have any questions! http://s346165667.websitehome.co.uk/psyktrans/dw.zip