Hi there, Sebastian.
I've had the same problem recently; here's what I did (not sure which Moodle version my institution uses, however....Hope this works on your version).
- Every time I create a new secondary glossary, I create a new category into it and I make sure that all entries I add to this secondary glossary fall into the category I've created. E.g. I create a sec. glossary for unit 2 of my course and I add the category 'Unit 2 vocabulary'.
- When I have finished adding terms, I click on 'Export entries' from the left menu and then 'Export to file'. An .xml file is generated.
- I then go to my main glossary, hit 'Import entries' and make sure the checkbox 'Import categories' is checked.
- I add my previously generated .xml file from, say, the secondary glossary of unit 2.
- When I'm done, my main glossary contains the new terms from the secondary glossary and because I have also imported categories, they're classified under the category 'Unit 2 vocabulary' automatically.
Hope this helps! Let me know if you need any clarifications.