Happy new year!
Version 1.1 of ThunderSync is now online. After some feedback from Israel I improved the vCard support and added an option to select the file encoding for import and/or export.
Download possible at https://addons.mozilla.org/de/thunderbird/addon/265058/.
Outlook seems to assume a certain codepage (8 Bits, 256 characters, depending on country) when encoding vCards. But vCards are meant to be written in ASCII (7 Bits, 128 characters, basic English). Everything beyond English characters has to be encoded separately after declaring an appropriate charset. UTF-8 would be a wise choice because the first 128 characters are identical to ASCII. But Outlook (or at least some versions of it) seems to use the system’s character encoding (Window-1252, …) without naming the charset.
So if some character strings are not correctly imported from or exported to Outlook: Change the encoding to your ISO or Windows codepage. Feel free to inform me about any bugs.