Hi,
First of all, you need a DDS degree or any similar degree from your country to be eligible to take a NBDE. Second you need to translate your diploma and transcription of your degree and make copy from all of them and send them to ECE.org . You can find the application for ece on there web site. This organization will evaluate your degree and by your request will send it to the ADA. Simultaneously with ECE, you need to fill the online application for NBDE on ADA.org and pay the fee, there is no extra fee for the exam but you are paying for evaluation. Then you should wait until ECE send the copy of evaluation to ADA. At this point you will receive an email form ECE. ADA will send you an email regarding your eligibility for taking the NBDE part 1. Thats it. But regarding your question about language, definitely you need to fill it in English, I can say even more, the exam will be in English too 🙂) just kidding.
In fact the process for being eligible for foreigner trained dentist and American dentist are almost same. The difference is that they will ask the university to send the transcription and other documents to them. but you need to evaluate you degree here. BTW, there are couple of others places that you can evaluate your degree, but ECE is the best one. all schools will accept that in the future.
As I said at the begging, you need to be a doctor at first for any further actions.
hope it helps
good luck
Hope it help