No, it is not a good solution to the problem; you ignore my earlier comments. English or latin text is not comprised of the sole ASCII characterset; it contains characters outside this set (quoting other languages, names, imported words for example).
Honestly, I do get your point about inappropriate use of regex, but this kind of simple text manipulation is well suited for regex. The biggest argument against using regex for this kind of problem is performance verses writing the same code programmatically in the host language (assuming you're using a fast AOT compiled language). However even that is a non-issue given the small quantities of text you're decoding.
Also I'd bet the regex in this instance would actually work out more readable because the transformations are basic so you're localising the text manipulation to simple rules rather than multiple lines of byte array reading and thus also potentially having to manually build in your own rudimentary unicode support too.