As I understand it, all the sentences may be used. But I don't understand when there is need to add "to be" after "is considered". Could you explain the nuances of these examples, please? For me, the first sentence & the third one are absolutely the same. (From Ngram I see that the first one is more common.)
French is considered the language of love.
French is considered to be the language of love.
French is considered as the language of love.
P.S. From my online course I have received a sentence: French is considered to be a language of love. I think it's a mistake because there is said about the certain category of language.