Least advanced English speaking TL

How backward can a TL be in it's technological knowledge and still have recognizable English as a major language (so I can fantasize sneaking technological knowledge into the TL)? Note that collapsing from war or plague would not erase knowledge, as long as a reasonable number of survivors are present.
 
I guess the easiest one is one in which, for whatever reason, the Industrial Revolution doesn't happen.

Early Modern English (Shakespeare/King James Bible English) is the earliest form of the language that a person from our era can easily understand. That's about how far back you can go making changes.
 
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