Can you measure a language?

A couple of days ago a friend of mine who lives in Germany (for now) asked me how long it took me to progress from level B1 to level B2 when I was learning German (my friend is a computer programmer and has an analytical mindset, so he likes to quantify everything). The question, apparently easy, gave me some embarrassement, and I still don’t know how exactly I should answer it. I don’t believe that language proficiency is so easy to quantify: of course there are tests, which you can take in several forms, written and oral, but I have come to the conclusion that no test is perfect and that the standard six echelon proficiency level assesement (from A1 to C2) is only one of the many imperfect instruments you have to estimate your command of a language, and that you should not care about them all too much and that a level of proficiency expressed in this way should not be your focus.
I have started learning German fifteen years ago, basically right after I finished school, and have been living in Germany more or less for the past ten years. Before coming for the first time to Germany I had been studying German for almost four years and I was under the impression that I had already achieved a good level of proficiency, but that was before I spoke to people other than my German teachers (theoretically, even before coming to Germany, my German was already at the C1 level, which means you can handle most situations in a pretty confident manner and that you write in German without horrendous grammar mistakes and you have a good command of the formal written language too).
It was before the era of smartphones, online translators, dictionary apps and before audio material in MP3 format became easily accessable for everyone. When you bought a book, you had a CD with some audio track and that was basically it. I did not have German friends. We had watched a couple of Hollywood films in German translations at university but I mean, after having watched the movies the couple of words I might have learned probably vanished very quickly. I started watching German TV just a few weeks before coming to Germany for the first time and at first I found it rather hard to get through the phonetic obstacle (I really did not understand much), but I was perseverant and tried to gain as much exposure to the spoken language as I possibly could in order to train my hearing with stuff more actual and meaningful than the few (very few) dialogues I had on my textbook CD.
I had however become friends with my German teacher and I engaged in long conversations with her, mostly in German. It helped that she was very very patient with me of course, almost like only a mother or a lover can be. It was all very different however when I landed in Germany, not only did I have problems understanding what the people were saying, they did not understand me! It had never really dawned on me that for them understanding me could be more difficult than me understanding them, but evidently my accent was too impenetrable for them and my vocabulary choice must have come across as extremely odd: Germans are not the most flexible of people and they do not seem to exploit the whole creative potential of their language or make wide use of hyperboles, like for example Italians do basically all the time in conversation – if an Italian tells to a German that he came “ten hours late”, which does not mean he came really ten hours late, but only “very late”, the German will think that he came, just like he said, ten hours late. I can easily imagine that an Italian would say of a woman that he fancies “I like this woman so much, I would rape her”, a German hearing this would probably interpret everything very very literally and call the police already.
Before coming to Germany I had already read Schopenhauer and Nietzsche in the original language, two of the XIX century heavyweights of German philosophy, which made me feel rather proud at my young age. This did not seem to help me much in everyday life however. Now I had problems when I went to the backery and I could not help people looking at me as if I were a complete retard when I asked for some information on the street. Some people switched to English with when I got an accent wrong and I found this extremely humilating. I had done rather well at pure theoretical language tests but I could not help feeling like a real dope sometimes.
So my advice to my friend would be: practise the language and use in everyday life until you feel comfortable in it. It may take a long time and it will require some strong nerves. Do not care the standard level assessment too much. A language is not a test.