If you'r updating from any web prior 3.9 to 3.9+ you need to convert your trl.xml files into po files.

This is done automatically during upgrade-script. There should be one po file for every supported language. If it's explicitly needed you can call the script directly via

php upgrade-to-3.9/trl convertTrlXmlToPo --trlXmlPath=trl.xml --outputPath="..." --webcodeLanguage="..." --targetLanguage="..."

If you'r planning to use kwf-lingohub you'll need to add trl folder to your .gitignore. If vivid-planet/vkwf is existing it's done during upgrade-script.

Next step ist to create a lingohub project