I decided to enter the Ubuntu App Showdown ! (http://developer.ubuntu.com/showdown/ and https://wiki.ubuntu.com/Touch/AppShowdownList)
I plan to write a dictionary/translation app : "uTranslate". The online engine will be provided by Glosbe.com, thanks to their simple API (http://glosbe.com/a-api) and their support of OpenSource (http://glosbe.com/a-api#H2_Share). Maybe future versions will handle other providers.
As the deadline is September 15th, it's already a difficult task ! And I have to learn nearly everything : QML, QtComponents, Click Packages !...
Well, the good news is that the online engine already provides the expected behavior : I can concentrate on design & coding of client app.