What you need is OpenType glyph substitution, which requires the use of a third-party program such as VOLT or the OpenType Compiler referred to in this Tutorial thread on Adding OpenType Features
You can create all of the glyphs in FontCreator, but adding the code to substitute the combined glyph when other characters are typed is not yet supported directly in FontCreator.
For example, in English, we need to combine f+f+i into a single glyph ffi — we can create the ffi in FontCreator, but the glyph substitution must be added afterwards. It is not too difficult to do using the OpenType Compiler.
If you don’t understand the tutorial you can ask here, though it is beyond the scope of supporting the use of FontCreator. You will have to work out the details for yourself. I have not used Microsoft’s VOLT, as it seems much harder to use, but there is a support forum for VOLT.