What language would be best for creating a mid-sized online game?

I'm planning on attempting to create a small 2d mmo at some point in the future. (The closest game out there currently to my vision is Puzzle Pirates) I've got an idea in my head, and was wondering what the best way to go about creating it is.

Here's what I need to be able to do:
The game must be playable on PC and mobile devices. (Android, iPhone/Pad) Preferably, it would be both downloadable and playable in browser.
The game will have many areas where player avatars can walk around together.
Players will have houses of their own to decorate with items.

What method do you think would be the most conducive to what I'm trying to make?

Java. Make it work in Java for the browser and then the Android version shouldn't be too difficult. Oracle is way behind in development but JavaFX was supposed to be the all-in-one solution for desktops to mobiles. So far, JavaFX is about 75% complete for Windows platforms.

First off, if you're asking this question you are nowhere near ready to even consider making something as complex as an mmo. I've worked on several and i'm telling you it is NOT as easy as people think it is. Second, you're not going to be creating one that will run on both PC and mobile devices properly. With current technological limitations on non PC hardware it just isn't going to happen for the time being - especially when it comes to android.

That aside, there's alot more to doing the whole customized housing than you think, I can assure you of that. That is a very, very complicated piece of code - I know, i've done it. Its also not something a non PC device is going to handle very well, memory wise

As my programming teacher in college said: start small