I am an UnderGraduate computer engineer student in Turkey in METU.
I hope I will finish next year.
My English is good but I am very poor at German. Are there any restrictions about language to work in a software company or to continue graduate education?
I have no idea. But why are you posting this in the Dutch forum? In this forum, you should speak Dutch.
yes the old misconception again : german is not dutch, dutch is a germanic language but dutch/nederlands/vlaams is not german at all. However since it is a germanic language their are simularities and people speaking one will often be able to understand the other (chances of it working in both ways are less). The most obvious language with some advantage in computer sciences is english....
the advantage of german I do not really know, the advantage of knowing dutch is poor I guess unless you are planning to work in a dutch environment.
Generally speaking (and I don't want to offend the exceptions readily available) the problem is bigger when you go into Holland - Belgians (dutch speaking) tend to have a wider span of languages they master (french, english and german) so they will pick up what you want to say.
It is nice manners though to learn the language of the population you visit (even on short term visits like holidays I try to learn as much of the new language as possible) it improves your experiences there, and broadens all your contacts - thus it is nice to do.