So, in English, if some one asks me “Do you want to travel to Japan,” I can respond with “If I had money, I would.” As I understand it(sorry if its not perfect), in Japanese that interaction would be 「あなたは日本に行きたいか？」、「お金があったら、日本にいく」
Here is my question: in colloquial English the “I would” bit gets dropped and we say “If I had money.” Can we drop the 「日本にいく」bit in my example? Or is there another structure we can use in Japanese for only half of an “If…” statement?
Yeah, in casual speech, you can just say お金があったら.
Follow up question. Is the use of か here common? My understanding is that the question particle is mostly used during formal speech, so in this case, since it’s not 行きたいです so か wouldn’t be necessary? Or is it optional?
I just wanted to put emphasis on the fact it is a question. I don’t think it’s necessary, though I may be wrong.
Yeah, it’d normally be left out, and instead spoken with a rising inflection, same as English.
Thanks! I’m still trying to get the hang of what gets added or dropped between formal and casual
I’d go a bit further and say don’t use the か in informal speech. It’s got quite a patronising/derisive tone to it. 「あなたは日本に行きたいか？」feels a bit like you’re scoffing at the person you’re talking to.
Yeah, it sounds so weird with あなた and being casual with the verb conjugation, but then adding か 
Also just answering “お金があったら” feels a bit unnatural and crude. Also a bit like there would be some relationship in having money that makes you want to go to Japan 
But in a real convo you most certainly would add something like まあ、ええ、行きたいけど etc. and elaborate a bit more.
Would it sound less crude if I used the ば form of ある instead of using たら?
Both can be used as a general conditional; not sure which one would be more common here.
I was more talking about the fact that the question is “if you want to go” so the full sentence then becomes 「お金があったら(行きたい)」Having money makes you want to go to Japan? 
This is just my gut feeling so take it with a grain of salt. I’m sure it would be understood.
Would changing 行きたい to 行きます be a solution?
Because now you’re saying you would go rather than you want to go
Yeah now I see what you mean.
I was thinking about the case where you omit the end.
I think this sentence is grammatically acceptable (more so than with お金があれば anyway), but it’s still unnatural because one’s desire to go to Japan isn’t determined by how much money one has. However, it really depends on how the person you’re talking to completes the sentence mentally. For example,…
I think this makes more sense, and that’s probably how someone else might finish the sentence if only the first half is said.
Generally, the ば form is more formal, so yes, perhaps. However, the main difference would be the emphasis that each usage has. ば usually places emphasis on the condition, especially if it has good outcomes, so I think that ば would actually be a little more appropriate here, even if たら is probably fine and very suitable for informal conversation.
I meant it as the mentally completed sentence when you only say お金があったら. But yeah, this is the exact point I was trying to make 