I've been mailing all day with author of this thread. Thank you Antii.

OK. I've got confirmation. This is Samsung issue and it's hard to do anything.
At the moment there is no fix for that. DatePicker is using some locales which are missing in your ROM.

You can easily check other apps using DatePicker - even apps from Google - not the Samsung. For example Contacts or People app.

Temporary fix is to change language in your phone to English for example.

And you need to waint until Samsung will fix this issue.

Good news is - I've tested today all devices from Remote Samsung Labs (remote connection to physical devices) and they are working OK. DatePickers are working OK. So in new version of Android this issue is fixed.

I'm playing whole day with it. I've even registered at Samsung Developers site to get access to devices. I've tested all of them. No issue. But they've got a little bit newer version of Android if this is Android 5.0.

I've Googled this issue and it's on official Android reports - but it's closed and marked as Samsung bug (not Google).

Mail me I'll send you a little bit changed .apk to test.

Could you send me an email (to this one from Play Store). I'll send you .apk and you'll tell me if it's working. I'm working on this issue but I can't test it because like I said I didn't have this problem.

I'm reading about it and it looks like it's Samsung issue. Looking for a workaround.

Thanks. OK. This looks bad. I can't reproduce it on my devices. I've got 5 devices. From Samsung at the moment S2. So probably this is something in newer versions of Samsung's API.

Of course this should be fix. I need to find what's going on.

Can you give me more details about your android version. Number from settings.

Thanks for your report. Finally I've got someone. I don't what going on with this. I can' reproduce this bug. Can you tell me full path - what are you doing. From the start of the app? This should be fixed.

Go to Stats screen to recalculate it. This is cache issue.
Stats will recalculate it again and you should have good values.

Yes. I'm using it the same way. If you want to use Fuelio in Slovak you need to switch your phone to Slovak.

There's no need to download them manually. Languages are detected by Android (this is how Google wants to be working). So if your language in your phone is English - you'll have English UI. If you language is German, you'll have German UI etc...

Insert it as new vehicle (with old data) and stary new log for current fillups.
You can easily create in Excel/Libre Office CSV and import it. Here's sample file:
https://dl.dropboxusercontent.com/u/6838779/2014-sample-fuelio.csv