Ask HN: Got job offer where I would downshift technically but upshift culturally

I have two job offers which are both good in their own ways and I struggle to choose between them.

Offer #1: Well-paid remote job at a startup, cool tech stack where I would learn a lot, but most likely stressful.

Offer #2: Well-paid remote job, irrelevant/outdated tech stack, most likely relaxed environment, and ability to practice and improve German at work.

Context:

I have been in the software development industry for ten years. I've worked for startups, small and larger companies, and bloody enterprises. During the last 5 years, I had technically challenging jobs, with a modern tech stack, and I was also improving my skills and trying to stay in the age. At the same time, I have been learning German as a hobby, reached a B1-ish level, and had a lot of fun learning it and traveling to countries where German is spoken. I would say learning a new language opens a completely new perspective to see a word and, without joking, makes you a different person.

It has become a bit hard to work at my current company because the founder would push us to deliver more and more, faster and of coerce with fewer bugs. Recently he was wondering why we still perform not well enough and told me that he knows people who don't stick nine-to-five, deliver on weekends, etc. He didn't say it meaning forcing me to work more, but more as a sidenote. However, I understood his point well, updated my CV, and got two job offers with salaries 50-70% higher than my current level.

Now I came to the point of deciding what to do next and surprisingly it turned out to be hard.

Normally, I would decline the second job offer or I wouldn't even consider it in the first place. But because of German, I went through the process. They are a small company producing goods. In the team, they speak German, and they wanted to find somebody with whom they wouldn't have to break the routines and have to speak English. They use SVN, Java 8, Vaadin, BPM tools, and some other stuff that is not relevant on the job market. It sounds like serious downshifting. But the more I think about it, the more I understand that it might be a cultural upshifting. There is no doubt my German would be at a new level after a year in the company and this on its own will make me a better person. At the same time, I doubt whether I would be able to do something boring for a long time understanding that whatever I have been doing in my whole career was already more modern than this.

What would you do if you were me?