I finally update my modified dictionary into firmware 2.15:
1 update kobo desktop to latest.
2 connect my kobo touch to my computer (my firmware is 1.9.17).
3 kobo desktop will prepare upgrade package for it.
4 under the .kobo folder of my reader, there is some file named dict???.gz.
5 open dict?.gz with a compressor (i am using 7z.exe)
6 replace files inside dict?.gz with my modified dictionary for 1.9.17.
7 disconnect ereader from my computer.
8 after all upgrade is finished, my modified dictionary is ready.