It's fine, and just needs the comma and an "and" before the second "with". So, "Master’s degree xyz with a focus on A, B, and C, and with a very good final grade." I agree that specifying the grade would be good, with the caveat that we know that comparability of international grades is an issue.

In a conversation, this would sound fine. In writing, though, using "with" twice does sound odd. It would be better to rephrase your sentence. I will add that usually, people don't care what kind of grade you got on your Master's. If you have a Master's degree, then mentioning the degree is enough. You don't need to mention your grade. The quality of the school is much more important than your grade, so it would be better to say something like "A Master's degree in X, with a focus on A, B, and C, from [one of the top research universities in the country / a major technical institution / etc.]" If you do want to mention your grade, you should include your actual grade, not just the claim that it was "very good." If you graduated with honors, you can say that. If you graduated with a specific (high) grade point average, you can include your GPA. Again, I don't think anyone will care about your grade -- but the phrase "a very good final grade" is meaningless, so you should either take it out or replace it with more specific information.

you can write: A, B, and C, and with. it might seem strange to put two and's together, but when reading aloud it is natural for us to say something like that.