Rather than environment one would say that the teaching language is Hindi / English or as the case may be.
Environment would have a different connotation.
As far as the word माध्यम is concerned, please note that in this context it ought to be explained as 'curriculum that is taught through the use of the XXXX language'. Also note that the word माध्यम by itself does not provide a full explanation. In my humble opinion it is माध्यम से that would be the correct translation.
Without being assertive about it, I daresay that usage of the word 'medium' in this form is not very common outside of the Indian subcontinent and English-language schooling/ education will be more easily understood. I would refrain from saying German or Portuguese medium school (unless of course your audience is from the subcontinent) and form a sentence with the formula XXXX-language schools/ curriculum/ education.
Please also see
http://en.wikipedia.org/wiki/English_Medium_SchoolTo sum up in this context other colleagues have explained the issue well enough.