Multi-languages and default to mp3

Features added

• Multi-language support: French and German are now added thanks to FtZPetruska and Mitsunee contribution.

Changes

• When you only download the audio of a video, it will automatically be converted to 320 kpbs mp3 for the sake of compatibility. Even if the bitrate is overkill, at least no one will complain about possible downgrade in quality.
• No more date and time at the end of the filename.

Fixes

• Fixed a bug when there already is a file with the same name.