Dear Redeye,
I agree that if the OP writes in English he should expect an answer in English. However there are also Germans who never learned English and they use Google translate or other translator softwares to get an impression about what the OP asks for.
When they answer in German they want to give the OP quick help but it might be that they feel unsure about the correctness of their sentences, and fear to be laughed at their try. Unfortunately this indeed happens sometimes by ignorant English native speakers from UK or US (not meaning you, no offense meant). Even our English teacher was shocked by some reactions coming from UK/US people.
For the German posts in the blueprint section you could use copy and paste the text into a translator software, too, to get an impression about what they wrote. I use that often (google translate) for other languages than German or English.
If you use the following search words in google (or whatever you use), you should find one which helps you a lot: translator german english
Imagine someone from e.g. Poland who had not learned English uses such a translator software to convert his question to English. Someone from Germany who does not understand English uses another translator to translate it to German (two translation activations, can you imagine how non-accurate this is in the end?). Now he uses the translator again to translate his answer from German to English, and the player from Poland uses the translator to get it from English to Poland language again. I assume that due to those double-translations some information might be misunderstood easily.
I think it would be better to write the answer in German, so that the player from Poland can directly use the translator from German to Poland language. You could do the same with the non-English texts.
Hoping that this helps a bit to understand us non-native-English-people better and have a good week