A simple way to convert files from other formats into SGF is to load the game into glGo and save it again as SGF. However, this will become a tiresome process if you need to convert more than a few files. To help with this, glGo includes an utility to convert a batch of files from UGF or Ishi to SGF.
On Windows you can right-click on an UGF or Ishi file in Windows
Explorer and select "Convert to SGF" from the popup menu. To operate on multiple
files, look into the glGo installation directory, by default
C:\Program Files\glGo. The converters are
ugf2sgf.exe and ishi2sgf.exe. Drag and drop a single game file or a complete
directory over the executable, and you will find the new .sgf files in the same
location of the original .ugf or .ishi files. Finally, you can use those two
utilities from a DOS command shell.
On Linux there are "ugf2sgf.py" and "ishi2sgf.py" commands which you can use from a terminal. Operation is available on single or multiple files and directories. See "ugf2sgf.py -h" or "ishi2sgf.py -h" how to use the utilities, or check the glGo SGFTools webpage for a more detailed explanation.