Hi !!!
I think that
Tessa is a lovely name.
It is simple to spell and pronounce in every language. It doesn't need any nickname. It has plain letters that are easy for everyone.
For example: I'm Italian but I have some problems pronouncing the R. I have a soft R (similar to the French R) that unfortunately is not what Italians use. So when I pronounce any word with that letter people hear that was not exactly correct.
Tessa is great in any case. Then it is good because it's a name without any particular religious connotation (the most of 'international' names actually have it).
Personal Name Lists
https://www.behindthename.com/pnl/125456