The package setup.py runs the lib3to2 converter for you on install, there is no need to run the converter manually.
The following (using my pip command installed for python 2.7) works fine for me; using pip is the easiest option:
pip install https://bitbucket.org/spirit/guess_language/downloads/guess_language-spirit-0.5a1.tar.bz2
provided that you have the enchant C libraries installed.
Alternatively, the following works as well, provided you have the 3to2 python package installed:
$ cd guess_language-spirit-0.5a1
guess_language-spirit-0.5a1 $ ../bin/python setup.py install
RefactoringTool: Skipping implicit fixer: collections
RefactoringTool: Skipping implicit fixer: int
RefactoringTool: Skipping implicit fixer: memoryview
RefactoringTool: Skipping implicit fixer: printfunction
RefactoringTool: Skipping implicit fixer: unittest
RefactoringTool: Refactored build/py2k/generate_data.py
RefactoringTool: Refactored build/py2k/guess_language/__main__.py
[..many more lines..]
Processing dependencies for guess-language-spirit==0.5a1
Finished processing dependencies for guess-language-spirit==0.5a1
but make sure you do that with a cleanly unpacked distribution (one you didn't try to run the 3to2 converter on).