I run a website that is a simple tool for a certain task. Right now it is available in english only. It attracts half a million visitors a month. It's mainly word of mouth, press and social traffic. Since it's a tool, there is no text content. So I only rank for very few keywords in search engines. Do you think I should translate the page in all languages? It contains only few words, so it would be easy. I could have a french version at fr.mysite.com, a portuguese version at pt.mysite.com etc etc. Have you made good experiences with this?
I've tried this with my website thinking it would be a quick way to expand my income, but it was not worth it. My SEO "juice" didn't translate much to my /de and /en pages. In my experience, you're more or less starting from scratch when you do this. And getting word of mouth and press coverage in a language that's not yours is not an easy thing. That said, what is your app about? I am a native French speaker and perhaps I could help you out.