Spelling of a Polish name?

While Tadeusz is in fact translated into English as "Thaddeus", I know a number of Poles whose first names are Tadeusz
but who refer to themselves in English by the short form of "Ted", in the US, an accepted abbreviation of "Theodor":-)

Actually, there is a very old Prussian first name "Thaddaeus", but unlike Tadeusz, it's been out of fashion for at least a hundred or so years:-)

My confusion was about comparing Teodor and Tadeusz. I'm sorry I didn't make it clear. We, non native speakers of English, find it really hard to get the message across.

Teodor as far as I know is the Spanish for "Theodor". Tadeusz is Thaddeus in English.
You probably know that the root "Theo-", dates back to the Germanic king "Theodoric" and is possibly the origin of "theodisk", later "TEdesco", Italian for "German", in German "DEUtsch" and in the ancient German given names Dietrich and Diederich.

In Swedish, Danish, Icelandic, and Norwegian, the somewhat similar "tysk", "tysker" etc. are closely related:-)

Teodor is of Greek origin - Theo is quite telling, isn't it?
Tadeusz is of Arameic origin.
Not everything is of Prussian or Germanic origin really.
I was referring to #30 when you for some reason compared these two.

Theoderic and Theodore are two completely unrelated names.

Theoderic is Germanic, from stems "theod" (not "theo"), meaning "people", and "ric", meaning "rule".

Theodore is Greek, from stems "theo", meaning "God", and "dor", meaning gift.

Any similarity is purely coincidental.

Oddly enough, there might be root connections there. Take Hungarian "haz" (house, home) vs. English "house", German "Haus", or Albanian "Ju" and English "you". Even linguists, among them Merritt Ruhlen of Yale, don't discount the distinct possibility of linguistic cross over from one neighboring language to another. In my two examples, lexical parity takes precedence over obvious phonemic differences, since each of the those words has in fact an identical meaning.

Surely, the above two names in your post are not utter coincidence. Language development is often murky at best:-)

Surely, they are utter coincidence. Despite superficial orthographic similarities, they are completely different and unrelated in every single way. There's no murkiness here.

See my private mail on this point.
We do agree on that, at least:-)

Coincidence is usually difficult to prove scientifically, as is the absence of said coincidence.