Short answer is, yes, you can use both.
But that prompts a question already mentionned above :
- why would you use both, or more precisely, which one should you use ? It depends on what you want to do now, and what you will eventually want to do
later, or
next year, or when you will get
FSX/P3D,
MSFS, etc. Now you want to fix runway lights, ILS, VOR, etc. in FS2004. Afcad (the program by Lee Swordy) can do that, and ADE (the program by Jon) can also do that. But let's say next month, you want to add a pylon, a generic building, and some taxiway signs on your airport, in FS2004. Afcad cannot do that ! ADE can ! Next year, you get P3D (or MSFS), and you want to change a taxiway lights and markings (and other things like you do with FS2004). Afcad cannot do that, but ADE can.
As Tom said, I also find Afcad interface lighter, a matter of taste, so it was hard to say goodbye to Afcad, go ADE and learn something new again. But, your goal drives the decisions you take. If you want to stay with FS2004 for years to come, and only do basic editing of airport layouts (runways, aprons, taxiways), then Afcad is perfectly fine. If at some point, you want to do more than that, Afcad just won't help you. Either you go directly ADE, or you install other tools to do other things (like grass around airport, you need SBuilder, but if you already used ADE, ADE can do that aswell, starting from FSX if I'm not mistaken)
I recommend you to directly use ADE. It is very similar to Afcad anyway, just start with the basic things you want to do, then later, learn more about the other things ADE can do over Afcad.
For language barrier, ask a question in Google in your native language (italian I presume) to find explanations in that lang. Example :
"ADE aeroporto aperto FSX"
That would give you results like youtube videos or forum discussions explaining you how to use ADE.