Diploma

Check Washington University in St. Louis, Columbia University, Pennsylvania State dual degree programme, Georgia Tech University dual degree program, Queen's University and The University of Western Ontario. There are many more, USA has many options.

Diplomas are not accepted, students must complete 13 years of education before they apply to German universities. You can apply if you meet one of the following 1. Completing the 1st-year of a Bachelor's programme from a recognized university in India in the relevant subject field.2. Clear the IIT JEE for admission
or 3. Passing the qualification assessment examination in Germany, called Feststellungsprfung.

Not really, your education qualification, relevancy of course, future plans will be more important. If you have completed 10+2, you should aim for a Bachelors and not another Diploma. In this case of course, visa officers will be curious to know what exactly you plan to do with your future.

Hi,
There are many universities offering lateral admission in 2nd year of B.Tech programme after Diploma from recognized institution or university.
But, for that you need to check the admission process and schedule for the same in different universities.
All the best!

Hi,
Yes, you will get admission but you have to go through the process for the admission. If they demand for entrance exam then you should appear for the exam and even they ask for language exam, e.g. TOEFL, so you should clear this exam so that you do not face any barrier in the process of admission.