Translation:We protest for freedom of Vietnam.
The English requires the use of the (freedom) because we are talking about a specific freedom, not freedom in general
It's not so much specific freedoms as freedom for specific places or people. "We protest for freedom of speech" or "We protest for freedom of religion" are perfectly acceptable constructions, but "We protest for freedom of African Americans" runs the danger of being misconstrued.
My friend, does it help anything??????? I reported many many fatal mistakes, nothing happened . Never. Ever. zero. Nil. Why to waste time ?
You could say "we protest for Vietnam's freedom" --from France, for example, or perhaps now from China. Or "we protest for specific freedoms in Vietnam", or even "the freedom of Vietnam"---in the sense of its independence. But this sentence makes no sense in English.
"Freedom" is an uncountable noun. But "Freedom of Vietnam' is a specific freedom. It therefore becomes a countable noun and requires an article. In this case it is correct to say " we protest for "the" freedom of Vietnam". Change it or don't change it. But if you don't, native speakers will continue to get upset.