If you have multiple glossaries in Transifex and you want to merge them, please follow the steps below:
Go to your Glossaries from the main navigation.
Download each glossary file you want to merge into a master glossary.
Click on the three dots icon next to the glossary that you chose to be the master glossary. Then click on "Edit glossary"
Upload each version of the CSV glossary files you downloaded in step #2.
Make sure to keep the “OVERWRITE EXISTING ENTRIES” disabled because you want to keep adding the terms from all these different glossary files you’re uploading.
Otherwise, you would overwrite the existing glossary with the file that is being uploaded.