plugins/qtwebengine/ffmpegsumo.dll isn't copied by windeployqt.
Also "qtwebengine_locales" folder is copied to wrong location. It should be under "translations".

Steps to reproduce:

• Open "Webengine Fancy Browser" example and compile
• Copy fancybrowser.exe to a clean folder
• Run "windeployqt fancybrowser.exe" from command line
• Create a file qt.conf in the same directory
  [Paths]
  Prefix=.
• Run fancybrowser.exe

See the debug.log:
[1215/102213:WARNING:resource_bundle.cc(286)] locale_file_path.empty()
[1215/102213:WARNING:resource_bundle.cc(286)] locale_file_path.empty()

Solution:

• Move qtwebengine_locales to translations/qtwebengine_locales
• Copy %QTDIR%/plugins/qtwebengine/ffmpegsumo.dll to plugins/qtwebengine/ffmpegsumo.dll