Insights from the Latin:
Some say that the King James translators (1605-1611) opted to transliterate baptidzo instead of to translate it, in order to avoid embarrassing the king, since he hadn't been immersed. Whether or not this is true, the fact is that the custom of transliterating dates back at least to the 5th century, when Jerome translated and standardized the Latin N.T.

The Latin Vulgate translation (begun 382 and completed 405 AD) of Acts 2:38 reads: Petro vero ad illos: Paenitentiam inquit agite et baptizetur unusquisque vestrum in nomine Iesus Christi. (But Peter replied to them "Do penance and let every one of you be baptized in the name of Jesus Christ.")

At once we see two problems: the substitution of penance (acts of contrition) for repentance, and the use of baptizetur for the original baptisthētō. 

The Catholic Church "baptized" (adopted) baptidzo into their language (Latin) as baptizo. Why? Infant baptism appears to have been occasionally practiced in the late second century, in cases of "emergency baptism" (when some parents feared their children might die lost). Yet it seems to have been rare until the 5th century.

By the 5th century, with the weighty support of Augustine (354-430), who drafted the doctrine of original sin to justify infant baptism, infant baptism became widespread.

In light of this it is hardly surprising that the Latin church chose to create a new word (baptizo) instead of using the normal words for immerse (immergere, mergere, or tingere)  -- as had been done in previous centuries when rendering the Greek.

Summary
The languages of the early centuries of Christianity initially (and correctly) rendered baptisma in words that meant immersion. Yet through the centuries there was a serious drift away from solid apostolic foundations. The medieval church bowed to the weight of popular opinion. The ancient languages illustrate this drift, and strengthen the position that baptism is immersion. And so -- yes -- those who want to be saved must still "wade in the water."

The third (final) installment of the Baptism series will be released next week.