Android APP internationalization

Hey developers and experts,

im from Germany and have coded a music note trainer app. Notes are displayed and you have to click the correct button (general description) There is a free version with basic funtionality and a PRO version with some extra features like pitch detection over microphone (with Fast-Fourier-Transformation...). I earn 150-200 Euros (net) a month only by selling the PRO version. BUT almost everybody is from Germany! Both apps are translated in English and partly in Spanish and Portuguese (in portuguese only store entry; in spanish only app resources (strings and graphics)). I have integrated Google Analytics in the free version and it shows me: I have around 1,800 active users now (April 2016):

1000 from Germany
115 from Brazil (portuguese)
100 form Austria (german)
90 from Turkey
only 78 from United States
56 from Switzerland (german)
26 from Mexico (spanish)
etc.

Free version downloads: 5000
PRO version downloads: 450+ (almost only from germany)

1) So, my first question is: Why so few english speaking countries downloaded my app (and in Germany so much)?
Its completely translated to english...

2) Secondly, how can i enter us market?

Some more questions:

3) Is the Play Store available in China? Or do i need to use different android app stores? How to enter there?

4) Which language they speak in Taiwan? Chinese and Taiwanese? Which language should i use for my app for Taiwan? If chinese, traditional or simplified? (There is to options in the Developer Console)

5) I have localized res folders for graphics and localized strings.xml files (for english, german, portuguese, spanish). And the store entry is in translated in these languages. What else do i need to consider for optimal internationalization?

6) Which markets are important to reach? According to AppAnnie i think: United States, Brazil, India, Russia, Mexico, Japan, South Korea, Taiwan, Germany and I think France, UK, Canada, Spain, Italy, and many more...
www.androidauthority.com/chrome-os-android-apps-play-store-689060/

7) Does an AdWords campaign on Play Store make sense?

I would appreciate your help very much!
THANKS

App on Play Store: Music Trainer Professional PRO

free version: play.google.com/store/apps/details?id=com.martins.martin.musictrainerprofessionallite
there you find PRO version

— modified on Apr 25, 2016, 7:25:34 PM