It's hard to say that it's absolutely wrong, but I agree with the other English speakers in the other thread that it's not very idiomatic, and that there ought to be several other better options. It's certainly misleading as the only translation offered.
The problem is partly that 'conquest' is a rather literary word already, and the collocation with 'self-' is even less common, if theoretically possible. Even in the most abstract, philosophical terms, it would sound better to me to use 'self' as a noun, maybe like 'the conquest of the self,' 'conquering the self,' etc.
And in more normal contexts, I would be inclined just to suggest a phrase with a verb; maybe something like 'overcoming one's own reluctance / (worst) instincts,' 'making a special effort,' 'forcing oneself,' etc.
I'll try to think about this again when I have more time and more access to dictionaries, but maybe others can take it from here.