Bit by bit should be accepted.
Should one always use an article for a language? We do say "parler (en) français", don't we?
It's not compulsory, it can be either 'parler français' or 'parler le français'. 'Parler en français' is 'speak in French'.
The voice said "Japon et portugais petit a petit". It did not say j'apprends le portugais petit a petit" I wrote what I heard. It was wrong. Now we have to read minds! LOL!
Are all languages masculine in French?
need to add 'bit by bit'
Bit by bit is an American colloquialism for little by little. Are the Duolingo translators perhaps English?