A few weeks ago I decided that our app is now popular enough to justify a little investment: get some (wannabe?) professionals to translate the app into the languages it's most used for. In our case the most popular languages were the following (vs. most popular across Google Play):
I think the big differences between our app and Google Play are caused by the target group of this app: only countries were the use of ODF (OpenOffice / LibreOffice) is widespread are likely to install our app in the first place. Captain Obvious strikes again.
Finding a serious looking translation service was actually harder than I thought - especially when the Google Play Developer Console puts a banner right in front of you: "Need help localizing your application?". Nope, that service seems to be dead now. A few weeks after signing up I didn't even get a confirmation mail or anything. Thanks for your help Google! So I went searching for an active translation service and found: tethras.com.
One thing that's really important before using a translation service is finalizing your strings.xml as much as possible. If you are about to rewrite and redesign your app I would recommend to hold off until the app is in a "stable" state. Also make sure to think about what could happen next with your app (feature-wise). If there's a new feature or the removal of an old feature around the corner, don't ask the translation service to translate the related strings.
After cleaning up my strings.xml I requested translation for Spanish, French, Russian, Italian, Polish and Portuguese. I've also requested to translate not only strings.xml, but our Google Play description and promo text too. All in all it cost me far under 400$ (about 70$ per language), which is completely fine for me considering that this is covered by our monthly earnings. It's an investment, which hopefully further spreads our app in the affected countries in return.
I speak German natively, so I went for the German translation on my own. In retrospective I have to say though, that the German translation would have been worth 70$ easily for me. Translating an app is such a pain in the ass!
One thing I completely forgot about though is telling the translators about the (stupid) character limitations in Google Play. I had to cut a few words out of all the promo text-translations myself (based on good-guess - I hope they're still grammatically correct).
Unfortunately using professional translation services seems to be completely uncompatible with something like crowdin.net, because you don't seem to be able to upload finished translations and ask users to improve on top of that. What I ended up doing was completely removing the languages I have translated from crowdin.net now...
If you're asking yourself why I'm paying for translation if I'm already using crowdsourced translation:
1. crowdin.net isn't free for everyone, so the monthly fee would quickly sum up to the one-time fee paid for professional translation
2. the internet is bad. I had users translating the app name (!) to "fuck you" or "test". Checking each and every submission is way too much work for me.
All in all I can say that I'm really happy with Tethras. I won't hesitate to use their service again for future projects.