"Is subject to" is also OK, but I'd like to offer some suggestions for the rest of your translation - no desire for points. Sometimes people think that I offer a different translation to be contrary. It's my way of opening up space to comment better on your question.

Contractions are two words run together. In this case, I think she's talking about "clipping" - cutting off the end of the word.

Here is a definition from Wikepedia:
**Clipping (phonetics) the process of shortening the articulation of a phonetic segment;**

(- not to be confused with the *lexical* definition, which means to actual shorten a word to create a new one. For example: omnibus > bus.)

This is how I would handle your sesntence:

"A rapid speaking style tends to undergo severe word-final clipping, resulting in a phonetic output strongly marked by glottalization in the case of consonatnts, laryngealizations, and nasal/laryngeal combinations in the case of vowels, which, along with the melodic effects of suprasemental tones, usually sound quite strange to unaccustomed ears."

word-final position … when a word terminates in final -n, ... basis for lexical creations **via some form of clipping**, presumably if they are salient enough, ...
www.ling.ohio-state.edu/~bjoseph/publications/2001wdrespons...