You didn't say it explicitly so you may not mean it, but I see variants of this idea floating around that the assembly language is somehow a major part of the books, or that you need to learn MIX/MMIX to read the books, or even that "Knuth wrote TAOCP in assembly language". The fact is that the vast majority of content in the book (even if you consider just the algorithms/programs) is in English.
As a rough measure, we can look at each volume's Appendix C—Index to Algorithms and Theorems, which lists every Algorithm, Program, Theorem, etc., and count the entries by their names:
Volume 1 (Fundamental Algorithms): Algorithm 86, Coroutine 2, Law 4, Lemma 2, Program 36, Subroutine 1, Theorem 12. Total content in assembly: 36 programs (over 652 pages)
Volume 2 (Seminumerical Algorithms): Algorithm 88, Corollary 5, Definition 14, Lemma 19, Program 18, Theorem 47. Total content in assembly: 18 programs (over 764 pages)
Volume 3 (Sorting and Searching): Algorithm 75, Corollary 2, Lemma 8, Program 33, Subroutine 1, Theorem 41. Total content in assembly: 33 programs (over 782 pages)
Volume 4A (Combinatorial Algorithms, Part 1): Algorithm 127, Corollary 12, Definition 2, Lemma 6, Program 3, Subroutine 1, Theorem 43. Total content in assembly: 3 programs (and 2 of these in Answers to Exercises) (over 883 pages).
I may have made errors in counting, but the point holds: If you don't like the assembly language just ignore it; it's a tiny part of the books. Knuth uses the programs when he wants to highlight some low-level aspects. ("Expressing basic methods like algorithms for sorting and searching in machine language makes it possible to carry out meaningful studies of the effects of cache and RAM size and other hardware characteristics (memory speed, pipelining, multiple issue, lookaside buffers, the size of cache blocks, etc.) when comparing different schemes.") This is not often, so most of the value of the books is got regardless of whether you read those assembly-language bits or not.
And in fact, as the chapters progress towards higher-level stuff (see the TAOCP pre-fascicles Knuth has been publishing in recent years: http://www.cs.utsa.edu/~wagner/knuth/), the proportion of MMIX is even less.