I just ran into this - it's actually triggering what appears to be a bug in PHP with SimpleXML. It manifests itself in really strange ways. However, I stumbled upon this using way more queries than it should, and fixing that seems to have resolved this issue.
This isn't something that I've been able to reproduce locally. It's possible it's related to the SimpleXML bug, but since your error is happening on template_list (which has a very strange version attached to it), it's hard to be sure; normally the issue goes back to the beginning of the XML.
Can you reproduce it consistently? Does anyone else have that issue with that language?
I had an error like this in the past only with special character for German languages. If I use (for example) an ü in the text it is showned as a special character in the XML after export. When I edit the XLM and use on one hand the ü and on the other hand the special character in the same phrase, I got an error overwriting the language and no error creating a new language.