I must also say that your percentage in your bachelor's degree is really outstanding, even if it was achieved in a not so popular university.
I don't think the study gap really matters. What matters is what you have been doing during those eight years after graduating with a BSc in electrical engineering. You mentioned that you are working as a lecturer at a polytechnic institute which is good. If you hadn't been doing anything fruitful during those eight years, that would have been a huge red flag, and the visa officer might assume you want to use Germany as a way of escape.
You also mentioned you tried pursuing an MSc in Japan, but you were unable to complete it due to some family crisis. Honestly, that wouldn't sound very good in the ears of any visa officer. What's the probability that a similar family crisis wouldn't arise which might force you to return home again if you are given the opportunity to study in Germany. If I were you, I wouldn't mention anything about my failed attempt to obtain a master's degree in Japan unless the visa officer specifically asks me about it which I highly doubt will happen.
You have been working as a lecturer at a polytechnic so that's a good motivation to go for a master's degree. It will help you advance your career.
Also, I don't think the reputation of your university really matters. The most important thing is that your university in Germany feels you are academically fit to pursue their MSc program in Electronics Engineering. The visa interview is just to test whether you are a serious and genuine student. They assess you as an individual. At that point, they don't really care about the reputation of your university.
If you are asked why you waited so long to pursue your master's degree, you can tell the visa officer that you wanted to make sure you were in the perfect financial condition before you made your trip to study in Germany. You can convince the VO that after working for those number of years, you have saved a substantial sum of money and that you won't run into any financial distress when you are given the opportunity to study in Germany. This will help you concentrate fully on your studies.