A professor of mine, who's native language is German and who is teaching a class in English in a German speaking country, suddenly answered an e-mail which I wrote in German (I'm a native German speaker too), in English. I'm wondering why he does that? What the proper way for me to react is, i.e., should I use English when sending him e-mails from now on?
I wouldn't worry about it too much: given the bilingual nature of his work, your professor probably context-switches back and forth between languages frequently. If the professor is very comfortable in both languages, they might not have even realized the switch, e.g., if responding to your email in the middle of a large block of work in English with their head in "English-mode".
If you want, however, next time you see the professor in person, you might ask if they have any preference for language in their communications with you: it could easily go either way (e.g., in English to make forwarding to non-German speakers easier, in German for personal comfort, or even no preference at all).
suddenly answered an e-mail which I wrote in German [...], in English. I'm wondering why he does that?
He might think that since the official language of the class is English, all communications should be carried out in this language. Or, maybe, if you're asking a technical question, he prefers to use English to avoid confusion between the technical terms employed during the lessons and the corresponding German terms.
should I use English when sending him e-mails from now on?
Given that the official language is English, this should arise no complain on his part. But you can also ask which is his preferred choice between the two languages, given that you are a native German speaker.
In Italy, I teach in a couple of courses which are taught in English: many of the emails I receive from Italian students are written in English, and I typically answer in that language. It's a good practice for both.
Explanation 1. For some reason the professor finds it easier to express a certain thought in English. As a native speaker of German myself, I often find myself in this situation. For some reason I can think of a nice formulation in one language but am unsure how to put it in the other. Also, e.g. when dealing with a student who could also be considered a colleague (student has a PhD or wrote a joint paper with the professor's colleague), in some fields the professor might be unsure whether to use du or Sie - a problem that doesn't exist in English. Or the professor wanted to reuse part of an email sent to another student. Or the email uses technical terms whose German translation sounds awkward.
In this case you can just answer in whichever language you prefer.
Explanation 2. The course is taught in English at least in part to make the German-speaking students get used to using English. Or at least the professor thinks so.
In this case it may be better to reply in English.
I would not interpret too much into this. I have to deal with such questions (in which language should I write an email?) almost daily in my function as an assistant professor. My native language is German, but I teach at a Dutch university (some courses are in Dutch, some are in English). With Dutch students, I usually communicate in Dutch (a language which I speak at near-native level), with international students in English - but when it comes to Germans, it already becomes complicated: It seems natural to communicate in German, but at the same time, although German is my native language, it is sometimes just easier to express a thought in a language I use daily in research (English) or teaching (Dutch or English).
Second, I sometimes write in a specific language in order to be able to forward, (B)CC or archive the mails. It's just not very practical if you cannot share something with a colleague because of language issues. Also the other way round, you sometimes copy/paste things without wasting time on translating things.
Third, I honestly am sometimes just unaware of the language i use. If I just have been talking in one language with a colleague, I might use that one in a mail that as well, without it being a concious choice. The hard part of working in several languages are not the languages themselves, it's switching between languages.
So, I would not put too much weight into this issue. However, it might also be that the professor wants to make a statement: I have some colleagues who want to make a statement by communicating only in a courses "official" language to avoid the impression that they would differentiate between students.
But, of course you can just ask what language the professor prefers. I get these questions occasionally, and - to be honest - I usually don't care too much.
I live in Germany since long ago.
On my experience, German are doing this mostly because 3 reasons:
- they won't worry because of your (for them) bad German.
- they are suspecting, your German is bad and maybe your English is better. It happens mainly on noisy phone lines, where they suspect mostly lingual problems and seldom acoustic.
- they only want to train their English (which they can't do with other Germans, but with a foreigner). Talking on German with a foreigner doesn't have any benefit for them, but talking on English means a possibility to a little bit of free training.
I think that the difference between the native and a non-native language is always very strong and prof always knew if they changed it. Maybe it is possible if he replied his twentieth mail on the day to his undergrads and all of them communicated with him either of German or on English with various levels.
In your place I replied to the prof on English, but mentioned on the first row some like this: "Ich würde gerne weiters mit Ihnen auf Deutsch kommunizieren" (I would be glad to communicate on German with you).