Did you consider putting the "center" of the detector somewhere other than in the middle of the vector? what would happen if you had 6 before, and 2 after, or 5 before, and 3 after?
Another thought I had: for performance reasons, it might be nice to have something more compact than a one-hot vector for each letter. Have you looked at determining sets of characters which have a similar impact on hyphenation, and encoding them together?
PS: do you have the extracted list of wiktionary hyphenations sitting in a text file somewhere that you could put up? I'm fixin' to quickly compare the accuracy to TeX's German hyphenation (once the 30+GiB TeXLive repository finishes downloading).
PPS: You could improve the display of code blocks in your site on desktop by adding
display: block;
max-width: 710px;
width: 80%;
margin-left: auto;
margin-right: auto;