So I have a language study visa for Germany (Type-D). In the "valid for" section in visa sticker, it says Deutschland. Can I travel to other countries like France with this visa? If not, why? Because shouldn't a visa issued by Schengen country valid for all other 27 Schengen countries?
Can I travel to other countries like France with this visa?
Yes, you almost certainly can.
If not, why? Because shouldn't a visa issued by Schengen country valid for all other 27 Schengen countries?
Yes in general they should. There are some exceptions but based on the information you provided, your visa should indeed be valid in all other Schengen countries. The reason it nonetheless says “valid for: Germany” is because it's a type D visa for a stay longer than 90 days.
You are only allowed to use it to go and reside in Germany for the length of your course. It is also valid for some incidental travel to the rest of the Schengen area (including any transit you might need to enter and leave the area) but it does not allow you
- to reside (= stay longer than 90 days) in any other country than Germany
- to spend the whole duration of the visa travelling the Schengen area
- to forgo the course and do something else entirely (if your plans change, you're supposed to apply for another visa)
Enforcement is not very strict but your trips to other Schengen countries must not exceed 90 days in any 180-day period and otherwise fulfil the requirements for short stays (sufficient financial means especially).
Because of these restrictions and the fact that long-stay visas are strictly national matters, I have never seen a type D visa that says “Valid for: Schengen states”. This marking is only used for type C visas.
Type D Schengen visa is mandatory for any foreigner wishing to study, work or live in a Schengen country for longer than 90 days (up to 1 year). It allows its holder to travel and stay in the Schengen area outside the originally chosen Schengen country for periods of 90 days maximum over 180 days and during the entire validity period of their visa. The travel purposes which can justify applying for a category D visa are:
- tourism or private visits
- professional activities
- to study, to take part in a training program or complete an internship
- family reasons.