I hear alot of whining about Duolingo's strictness in marking the student responses for translation. Yes, there are inconsistencies and equivalency issues to be debated and argued, but this is how I see it: Duolingo leans heavily toward literal translations because they want you to demonstrate that you understand 1) the meaning of each word or particle in the phrase or sentence and 2) the role that is played by that word or particle as it contributes to the syntax and construct, and overall meaning. I am in total agreement with this as I attempt to understand the language and its evolution to its present day form. Frustrating at moments?...yes!... but I know that this path has the best chance of getting me to where I want to go.
I sort of agree with you, although don't blame "DuoLingo". There are people working very hard to think up all the possible translations and them list them in their end of the app.
I wanted to say "can't" or "won't break", which is pretty equivalent to your "unbreakable", because "doesn't break" implies that someone is trying hard to break it.