What are some resources for speeding up learning of advanced German mathematics-vocabulary?
A formal approach would be to start with the internet documentation for common core-standards and curricula (Rahmenlehrpläne) as implemented in a particular city or state in Germany, e.g., Berlin. Chrome will automatically prompt you to translate the page I've linked to. Table 1 of that page organizes these standards by subject/grade-level. From there, you need only look for key terms and translate.
A quick reference approach would be to Google translate a particular term and to Wiki its translation in the target language, i.e. German, and then to repeat with neighboring words in the target article until the context becomes clear.
I learned quite quickly by browsing through this book: https://www.springer.com/de/book/9783322943804
Above you confirmed that you are addressing graduate level mathematics. In this case, my recommendation is to get hold of one or two well-written textbooks on core topics. Here are some examples:
- Ben Schweizer: Partielle Differentialgleichungen
- Folkmar Bornemann: Numerische lineare Algebra
- Christian Hesse: Wahrscheinlichkeitstheorie.
In this way, you will pick up the vocabulary much faster than with any word lists or dictionaries, and you will get a realistic feeling for mathematical writing in German.