I started this question in this forum, but in german language - bad mistake, as the answers were in english. To make the answers usefull for everyone who might need the information, here comes the starting message again, but in english and a link to the english part of the thread:

A questionnaire that still works under Limesurvey 2.05 should be migrated to actual Limesurvey 5.3.31. Import wiorks fine, but

- An individual template ist used and stored in limesurvey/templates at the old server
- No such directory is found on the new server, but "limesurvey/themes" instead.
- Template format at the new server is completely different from the old server.
- Manually created directory limesurvey/templates and copied the old content into it - with no success.

Question was, if there is some documentation about how to convert old format to new. I couldn't find any and would appreciate any help.

The question is answered already here (in english):
forums.limesurvey.org/forum/installation...sion-%C3%BCbernehmen

Thanks to tpartner and holch
.
Greetings
Erich