Are you familiar with compiler technology? Lexers, parsers, ASTs, code generation, etc.? If not, start by reading something like
https://en.wikipedia.org/wiki/Compilers:_Principles,_Techniques,_and_Tools; that should give you some grounding so you know what you're getting into.
http://www.ethoberon.ethz.ch/WirthPubl/CBEAll.pdf is a somewhat shorter starting point.
Would this tool also generate actual code? Or should it just point out the syntax errors? Generating code adds a bunch of complexity; creating ready-to-run executables even more so. If that is part of it, I'd estimate that you have no chance of finishing within the next 12 months. If not, you may be able to get something useful out within a couple of months.