po: update Japanese translation
po: update German translation
FlightLogger: reset in constructor

Fixes valgrind warning.
NMEA/Attitude: Provide possibility for checking if heading is usable

For the internal "fallback" calculation of the heading heading_available
is never set to true. It is also not possible to set this to true since in
that case the recalculation would be skipped until it expires.

Provide an additional flag to allow checking the "usability" of the
heading regardless of how it was obtained.
GlueMapWindowDisplayMode: Use AttitudeState::IsHeadingUsable()

Fixes a regression introduced in
commit 337a60908c21e7dbd308d3d21be5a7308a1012fa
TrackLineRenderer: Use AttitudeState::IsHeadingUsable()
RowFormWidget: use AngleDataField in LoadValue(Angle)

This method was never worked ever since we added AngleDataField, but
fortunately it was never used.
WindSettingsPanel: automatically re-enable manual wind controls

.. when the user disables "Prefer external wind".  Fixes TRAC #2336.
dlgAlternatesList: implement CanActivateItem()

Allows double-clicking list items.
FLARM/Friends: check for nullptr in GetFriendColor()

This runtime check is necessary because the DrawThread /
MapWindow::DrawFLARMTraffic() may call GetFriendColor() before the
main thread loads the traffic databases.  Fixes TRAC #2669.
release v6.5.2
NEWS.txt: prepare version 6.5.3
CrossSectionWindow: rebase on AntiFlickerWindow

Eliminates flickering in the cross section on Windows.
Util/CharUtil: add IsASCII(unsigned char)

Suppress potential "ambiguous call" warnings and eliminate two casts
that are now obsolete.
Util/UTF8: use IsASCII()
Util/UTF8: move code to IsLeadingN()
Util/UTF8: reject invalid leading byte
test/TestUTF8: unit test for our UTF-8 library
Util/UTF8: add CropIncompleteUTF8()
InfoBox/Data: crop incomplete UTF-8 sequences

Fixes JNI crash on Android with Hebrew InfoBox titles.