Full, native support for Chinese text is not impossible, but it would add enormous complexity and is not on my roadmap presently. I apologize for the inconvenience.
Decker is both a native application and a web-based application. For portability and consistency, it travels with its own routines for text layout and string manipulation, as well as its own bitmapped fonts. Ideographic languages would require very large bitmapped fonts, which would also be very difficult to design, and which would considerably enlarge web-decker builds: including the Unicode lookup tables and CJK glyphs for the built-in fonts could bloat baseline web-decker to 10x its present size or more.
Certain workarounds are possible: you could replace existing accented characters within Decker's character set with alternatives in order to represent new character sets; see All About Fonts and the included font editor. For somewhat more natural text input, you could modify the lookup tables Decker uses to ingest UTF-8 text in order to map the Unicode equivalents of your modified characters to DeckRoman indices, but this would require familiarity with C and JavaScript.
Decker is open-source and permissively licensed, so anyone with a sufficient technical inclination is free to explore even more radical modifications in their own fork.
