ti vs. di
Chinese and English both do not have voiced alveolar stop. "t" and "d" is distinguished by aspiration. Therefore, when translating to English, simplity t->t, and d->d is OK. The former one "t" is an aspirated voiceless alveolar stop, while the latter consonant "d" is an unaspirated voiceless alveolar stop. In standard IPA, they should be written as
However, Dutch is a different story. Their "t" and "d" are both unaspirated, and they are distinguished by voiced/voiceless. In IPA, they are denoted as
[d]. Therefore, for Dutch speakers, a Chinese "di", which is voiceless, sounds like "ti" to their ears.
Chinese pronunciations of "狄"
Chinese pronunciation changes over time and space. There is never only one pronunciation given a character. There are ancient phonological dictionaries, but they only told us the classification of characters in terms of their pronunciation. Although there are many research working on investigating ancient phonetics, for actual way to pronounce in a certain historical time at a certain location, there's no absolute answer.
The closest answer to your question may be found here: ytenx.org. For the pronunciation of Tang, 《廣韻》 is maybe the best source to refer to. For 18-th century Chinese, 《洪武正韻》 is the book you need. Related contents are listed below:
徒歷切 <- This is the pronunciation
荻小韻 <-This is the classification
定母 錫韻 四等 開口 <- This is property of the consonant, voxel, etc.
Most researcher believe it pronounced as
/dek/ (near the capital city Chang'an).
杜歷切 <- This is the pronunciation
入聲七陌 狄小韻 <-This is the classification
The pronounciation is much like the contemporal Chinese. In northern China, it's "dee", and southern China "dik" or something similar.