I think that preparing your app to support multiple languages is the important part. You can successfully do that by adding one extra language ( besides English ). For North America add Spanish.
Now your app is structured properly to use text from languages files ( and not hardcode in code ). This allows you to send the English file to a translation agency, get it translated in another language and add the the new language to he mix.
You should do that in subsequent versions of the app. As you see the need.
If you need more technical info on how to do that, feel free to schedule a call.
Good question, but my feeling is wrong time to ask it. It's hard enough to get users, period. Getting users in your home country is going to be much easier than a foreign country (I'm assuming you're a US based company/founders). Now, there is a time when I would absolutely look at language support for other countries, but there is so much to learn about your product, your users, your customer acquisition and all that jazz before you go and build out the code to handle different languages.
Now, if you are building a really basic app that is easy to translate, then maybe. But if the app is going to be a reasonably sophisticated social app, with at least a few bells and whistles, it may be more than you want to take on at first.
If your target market is North America, then there's negligible motivation for going beyond Spanish and French as secondary languages.
French would only apply to a relatively small part of Canada; but it might spill over across the Atlantic, thereby giving your app an entrance into other parts of the world through social sharing.
Spanish is much more important -- not only because Spanish is used worldwide by a staggering number of people but also because Spanish is fast becoming a crucial second language here in the USA. Witness these statistics:
35 million Americans speak Spanish at home (2009)
76% of hispanic Americans speak Spanish at home (2009)
50.5 million hispanic Americans in 2010
16.3% of Americans in 2010 are hispanic
132.8 million hispanic Americans by 2050
30% of Americans by 2050 will be hispanic
Although few people listen to me, I always advocate for more attention to be paid to the Latino / Hispanic U.S. market. That's reflected in some of my own initiatives behind the scenes as well.
I don't necessarily recommend focusing on multilingual marketing right away. As others have advised, stick to the English-speaking audience initially. You'll have challenges enough early on without complicating matters by injecting translations and extra marketing channels into the agenda. English is your proof of concept, your test case. From there, expand.
That said, you should pay special attention now to how your brand name may facilitate or limit expansion into other language markets. All future possibilities should be taken into consideration at the moment of naming. That includes potential overseas marketing, the addition of new service / product offerings, and the very real possibility that you'll pivot and redefine yourself as something else -- foreseeable or unforeseen.
As a professional namer / domain investor, I'm not a localization consultant per se. But language factors into my daily routine. Last week, for instance, I wrote emails in Arabic and Spanish and had to fumble through a smattering of French, Italian, and Portuguese in my inbox. So maybe I can offer a useful perspective on your branding and marketing.
If your application it's available only in North America App Store, you can get some stats by asking your users some details - like their native language (if you're using a registration process, that's easy to do).
If your application it's also available outside US, you can easily track the number of downloads for other countries like France or Germany.
Based on this stats you can make a decision, it's easier if you can actually see some numbers.