Also the more you speak the language, the better you get, so by making the effort to speak German, you will make yourself better at the language simply through the practice.

German chiming in here: I disagree with the 2nd part of your answer. Computer work is first and foremost english by default. The company hired this person fully knowing he doesn't speak German. Meaning: His colleagues are trying to sabotage him by speaking a language he can't understand which in turn is hurting the company. Speaking english as a tech person isn't a 'courtesy' it's something you should be perfectly cabable of and comfortable with. If they wanted to help him they would ask him to talk in german while they continue to speak in english. This is just idiots being idiots.

@SteffenWinkler German software developer here, none of my colleagues speak fluent english. The most you'll find here is english subject matter terminology used in a german conversation

@Magisch some of my colleagues aren't fluent in it as well but everyone can speak it well enough to get 'the point across'. Even if it takes a few attempts. I formulated my comment a bit hyperbolic, I admit that.

@SteffenWinkler Generally I agree with you btw. I think OPs colleagues think he doesn't fit and don't want him there so they fall back on telling him essentially the equivalent of "sod off" when he tries to ask questions. Not nice people methinks

They don't have to do that I mean sure, if you want to be counter productive. OP clearly has difficulty putting things in order. If someone asks me to speak in english instead of dutch I'd happily comply to prevent any miscommunication you might have. It's a business after all, not much room to make many mistakes.

@Edgard I totally don't agree with you, sorry. As interviewed in English in the first, and no language requirement, and having some customers talking English only, then English in the work is somehow required. There is no obligation to talk with me in English, but I can do the same as they do (in French for example), and then we have a language madness in the work. Also I have this problem only with 2-3 coworkers,

Reading the OPs question I get the idea he has an attitude problem. He expects that others do what he wants. And if they don't do what he wants he calls them racist. It's not too difficult to understand why the other people don't do all the time what he wants.

@Edgar I think he means discriminatory not racist. If you speak in english and then get a reply in German I do feel like they are doing it on purpose. Obviously. Consistency is key though.

@Edgar you got it the wrong way around. The company asked a non-native speaker to work for them. It's the companies and the job of his colleagues to enable him to do his work.

@MosCH: If you think using French is the same then go ahead and do that. It won't take long before someone will explain to you your error in thinking.

@Edgar MoshCH's analogy is completely correct. If everyone speaks in their native tongue nothing gets done.

@Edgar you misunderstood me, I never obligate anyone to talk a language which I can understand (the opposite, I am trying always to understand them before I ask to explain in English). We have big customers (such as Ferrari), and we have really so much hard rules to care about, so any misunderstood of those constraints can f**k everything up in the company, for that I am asking sometimes for a clarification in English.

In my work contract/chart, if you make something wrong, this point can lead your to jail, and it is you problem to ask your colleagues about clarification when you don't understand somthing.

@MosCH: You write "How to tell these kind of people to explain in English instead of German, without being rude?" And you are surprised that "these kind of people" react in the way they do?

I am asking about a way to tell them, as all the ways I used was not working (I never was rude, and even when they are ignoring me, I just do like nothing happened).

@northernGateway: It seems you didn't even read the first three words of my answer. It is not surprising that you don't understand it. If you feel like down voting my answer that is perfectly alright. But to be fair you should read it before you down vote it.

@NajibIdrissi It isn't a matter of opinion. Why do you hire someone that doesn't speak fluently German? If you are going to communicate work cases you need to be sure there is no miscommunication. Because if you do, not only do you undermine his work, you will lose time and the company loses money. If OP is hired on the idea that it's an "international culture" then I at least expect them to speak English. If not, then OP is duped. I'm a programmer, if I join a company that doesn't speak English, but was told it does, ill be leaving the next day. It doesn't take effort really. It is EXPECTED.

"Why do you hire someone that doesn't speak fluently German?" Because they expect him to integrate himself and learn the language. Germany is like France; don't expect to manage in everyday life only speaking English. Insurance, taxes, appointments for your visum (seems OP isn't necessarily EU-citizen), problems with police: this isn't Scandinavia, where everyone speaks decent English.