activities, minor runtime warning removed

there is a race in some case when we refer to the main or the activity object.
Messages, added info that we have utf8 strings

Not sure why but some users require this option but not all.
android build, removed unexistant qtmedia_audioengine

This library was required but does not exists.
fix translator comment

The correct way to make a translator comment is //:
translations, removed vanished translations