When 5.10 will be released I would like to check my translation again in jabref itself by running 2 instances next to each other. Left the English version, right the Dutch version. Is this possible in windows 10 and how to do this?
Yes, it is possible to run JabRef twice at the same time. You can simply install the latest development version that DOES NOT include the dutch translation yet and then later also a version that DOES have the changes included.