Usually English documents e.g. Birth Certificate, 12th Standard, BA/MA etc. are accepted for the Visa process unless otherwise stated on the website of German Consulate / Embassy.
The original Visa cannot be changed. After expiry, options for extensions or application of a new Visa are available. Please check with the relevant authorities for the same.
Migration laws in Germany have eased since 2024 and after living and working three years in Germany one is eligible to apply for citizenship. Please refer to the relevant authorities for the same.