Hi there! I am interested in Nursing in Germany like you are except I do not have a nursing degree and I am choosing to try and go through an Ausbildung as a Nurse. I can only tell you the information that I know based on Germany's requirements for Canada. I cannot speak for Singapore as they may or may not have different rules or regulations. Your Germany consulate in Singapore will be able to give you the correct information if there is something different or extra that needs to happen.
For the language: I was enrolled in a school in Hamburg called DeutschAkademie. They have online classes. It is exactly like being in actual school except it is online on Zoom. I took A1 to C2. This took a year. The classes are very intensive 3 hours long and you move very quickly. I had purchased a Goethe institute course online and that did not suit me. I liked the DeutschAkademie because there was structure and deadlines as opposed to Goethe where you can complete it in a time frame. For me when I have 3 months or 6 months to complete something, it never gets done. Just a suggestion if you are looking for some serious learning.
As for being a Nurse: Being a Nurse in Germany is heavily regulated. You will have to have your transcripts, certificate, any high school grades, everything related to your education will have to be translated into German. This is necessary because they have to make sure that the education you received is equal to Germany's education. I chose to go through an Ausbildung because I wasn't sure if I got a nurse degree in Canada if it would be deemed good enough for Germany. We do not do things the same. With the Ausbildung you work and get paid and you learn at the same time. In Canada, you are not allowed to work until you have your degree. Of course you do have clinicals but this was such a different system so I never got a degree in Canada. Even if you do an Ausbildung you still need all of your grades and certificates translated. I have been waiting 3 months and still not have received my translated documents yet. This all takes some time.
It depends on the hospital you apply for. I have seen B1, B2, and even C1 requirements. Of course the more you understand the language the more successful you will be. I feel that getting the highest language level is very important.
Also, the Bundesagentur für arbeit is a really good place to talk to about jobs and requirements. I found that the German consulate in Canada is only really good for giving you information about visas. They didn't give me any good information from the questions I had about Ausbildungs and nursing in general. I have gotten so much information from Bundesagentur für arbeit in regards to the Ausbildung and they know the process on how to become a Nurse.