No matter how proficient we are in foreign languages – our native language is always more personal/intuitive. That’s why I for instance still choose the Russian version of web-sites over the English or German one. It’s not easier to read, but it seems somehow more personal. So I don’t see a reason to build up a barrier between your content and a client at the beginning of the journey.
Seemingly, everyone speaks English in business. Moreover, every person is sure that he has a highly proficient level of English. However, even in this case, there still might be small nuances that might be misunderstood. These misunderstandings will end up in an awkward situation.
You cannot allow yourself a mistake in English. Your content should be perfect. A mistake in German might be excused because you are trying. That pertains also to the style of the language: the use of «simple English» or of a very sophisticated style or obsolete phrases is inappropriate.
By using English, you immediately position your company as a foreign and international one. It’s great if it’s true, even more so if your company is founded in a country having a positive image in Germany. But if you’re starting from the post-Soviet region, then using English might raise concerns.
We have all heard the phrase by Marshall McLuhan: „The medium is the message“. A message to your market and clients not only depends on the chosen words and the chosen tone but also on the choice of language. By using English, you’re showing that you’ve spent too little time exploring the local market. Way to go, if you want to talk about customer-oriented marketing and business. You just cannot be customer oriented and ignoring his basic values.
Surely, the quantity and quality of your clients may influence your decision. It’s up to you: are these clients worth translating all the texts and creating new content?
It is for you to decide what image and information of your company you want to convey. The last point is again about your target audience.
If your target audience is people at the international level, who are fluent in English (they are most likely modern expats in Germany) and are positively inclined towards business with companies in your region, then you can leave marketing in English. In other cases, I suggest you to switch to German.