If it's a startup, I'd think twice. There's no guarantee that you'll be happy at the new company, especially if it is not profitable.

Bureaucratic stuff can take time in Germany. Learning the language can challenging. The language schools have very different quality of teaching.

London has a much larger population of immigrants from the Middle East. So if your prospective employer in Berlin had a London office, or business ties to the UK, that would be a plus.